Never thought we'd have a potato talk about that scene
Regarding the sergent's face, I would not define it as angry, but more so like highly overstressed/concerned. That mixed with him facing those giants and losing comrades multiple times.
I totally feel he's more miserable than most of the recruits. And that's why he shouts so much, and gives the illusion he's so harsh.
I wonder if it'll be important in the long run. But he seems to have links with Eren's father afterall.