It's disputable whether any such limitations currently applied to AlphaStar are really working as intended. There has been some controversy over it. I saw the matches and it did seem that some of the actions taken by AlphaStar would not be possible to do by a human. Human APM is limited not just by the mechanical speed of one's hands, but also by the mental models that exist in one's brain. Muscle memory can't do everything for you. But in AlphaStar's case, it can perform every type of action as if it were done with the speed of muscle memory.

The original commenter's remarks about TTFA seems to be equivalent to what I'm referring to.

Relevant reading: https://www.alexirpan.com/2019/02/22/alphastar.html