TL;DR: The original concept art presented a being that the brain can rapidly categorize as intelligent and a likely threat, while the updated concept art makes us hunt for the being's eyes so we can gauge its intelligence and categorize it.
I want to bring attention to the importance of color in the model. I have very little experience with art and human psychology, so most of what I will present is only the result of my hypothesizing and guessing. For the sake of argument and simplicity, I will temporarily consider humans to be an animal within this post.
1) Eyes are key.
Have you ever noticed that you will constantly keep aware of anyone else who looks like they may be staring in your general direction? You keep looking at their face to see if they're looking at you and you get a nagging feeling whenever you look away. You constantly want them to look at you so that you know they recognize your existence and you can stop using your brain to track their movements. Perhaps you look in the direction they're looking to see if you're missing something.
You've probably heard that "the eyes are the doorway to the soul." Indeed, humans often seek to lock gaze with each other. Have you noticed that you are instantly able to spot the person staring directly at you? Your instinct is probably to whip your head around and stare back. This can lead to awkward moments where the person who was staring first tries to break eye contact as soon as they realize that you're looking at them. Other times, you stare at each other for a comfortable amount of time and then look away to go back to your prior task. In both of these cases, you look to their eyes for signs of information and intelligence.
2) Intelligence.
Intelligence can be generally understood as understanding one's surroundings, forming expectations about those surroundings, and acting based on those expectations. Both body language in general and the state of a being's eyes in particular are important for determining an animal's intelligence through observation only.
2a) Body language:
How does the organism react to its surroundings? Is it calm, yet alert? Does it move stiffly and react rapidly to any change as if constantly afraid? Is it twitching to a new position often to check its surroundings?
We generally attribute higher intelligence to animals that move deliberately and with confidence. We subconsciously study them and come to the conclusion that they know something we don't. Or, we at least single out the calm and confident animals (often predators) as being more intelligent than other animals around them (usually prey).
Please note that, if intelligence is quantifiable, then both predator and prey may have the same level of intelligence, just intelligence used in different ways. The species of prey are constantly scanning the world around them to spot dangers, while the predators only have to focus on the prey in front of them. Species of prey only need to understand "flee from danger", while predators only need to understand "chase, kill, eat."
2b) Eyes:
Eyes can be further divided into physical traits and use.
Physical traits include size, location, and structures within the eyeball. Predators have eyes located on the front of their head, while prey have eyes located on the side of their head. Humans connect the attributes of rapid and twitchy movement, location of the eyes, status as prey, and perceived low intelligence to more easily categorize animals they meet in the future. Similarly, humans connect deliberate movements, forward-facing eyes, status as predators, and perceived high intelligence as another category of animals.
Size and structure of the eye also are analyzed to gauge intelligence. Generally, large eyes and proportionally large pupils are seen as having lower intelligence, since they need to take in as much information as possible, rather than using smaller eyes and pupils to focus on details and extrapolate.
Use follows from structure and also takes speed and accuracy of eye movement into account. Humans equate higher speed and accuracy with higher intelligence. High intelligence allows the animal to use their other senses to locate a change in their surroundings and rapidly move their eyes to focus on the exact spot where the change was located. Similarly, animals that react slowly and take time to search for a detected change are considered slow, a.k.a. retarded, a.k.a. not as intelligent as other species. (I use "retarded" here since literally means "slow". It is meant purely as a descriptive term and not as a derogatory term as it is commonly interpreted today.)
3) Interaction and groups
Possibly less important than the other sections, this refers to how an animal reacts when within a group of other animals from its same species. The comparison I will make here is between wolves and bears. A group of bears can be a fearsome thing, but they don't typically hunt together and, depending on the species, may not need to hunt. Instead, bears can forage for fruits, nuts, and berries. Meanwhile, wolves hunt in packs. They work with each other to chase, corner, and kill their prey. This - arguably - takes more intelligence than a bear hunting for its food, since the wolves have to constantly figure out where the other wolves are and how they can force their prey to move in a certain way.
4) Color
Finally, we are here at the point I originally wanted to make, but felt I somehow needed to justify. Comparing the two concept art pieces we have for the Tsi-Hu, I noticed a general feeling that the more recent concept art depicted a less intelligent enemy. Here are the renderings for reference:
Let's start comparing factors for perceived intelligence.
- Human familiarity. The original appears more humanoid than the updated concept. Humans generally perceive other humans as being intelligent, even more so when comparing humans with other species.
- Cloth/clothing. The original has a cloak and, if you look close enough, armor. The updated version has parts that look like they could be armor, but there seems to be no clothing present. The lack of easily identifiable clothing means little on its own, but is a stark contrast to the presence of some form of clothing in the original version. Clothing means intelligence, since humans rarely see any other animal creating clothing. Clothing is a uniquely human thing and requires reaching a threshold of knowledge, situation, and intelligence.
- Skin color vs environment color. Blue skin/armor seen in the original concept art seems to match much better with a planet covered in ice with some volcanoes than the "earthier" tones present in the updated concept art. This is a largely frozen wasteland and using camouflage seems much more intelligent than not using camouflage.
- Eye color. This is the entire reason for the three, numbered segments about eyes and intelligence. This one point. Look at the original and notice how you can immediately focus on the Tsi-Hu's eyes. The bright red contrasts with the blue and light grey of the armor, the brown of the cloak, and the environment.
Now switch to the updated concept art. Notice how you have to search the Tsi-hu's head for familiar silhouettes, head shape (spikes are generally unfamiliar on humanoid heads), and facial structures before you can find the eyes. The pale blue eyes blend almost too well with the sandy color of the Tsi-hu's face and armor and the grey background color. That time spent searching for eyes is time that the brain spends trying to gauge intelligence. We are trying to lock eyes with the image on the screen, but we just can't do that fast enough.
Aaaaaaand there I go again writing another "scholarly" paper after midnight and without any research.