The OVA suffered from a serious lack of Earphone Jack and Pinky. OK, I guess that Jiro had her moment last season... But we still need more Ashido.
Aizawa also comes off pretty cold in all these saying that he's not gonna intervene for the sake of the test
Overseeing a practical is... Not easy. (BTDT) You want to step in like you would in a lab or ordinary class, but you can't. Doing so would invalidate the exercise as the whole point is seeing what the students do (or don't do) on their own. When the practical involves physical danger, it's even harder because you have to let them get to being just shy of actually being in danger... And then intervene before they're actually in danger.
Of course, since his students are superheroes Aizawa can let things go rather further than I could. Learning to evaluate and deal with being in a certain level of danger is a key part of the excersise.
So, I kinda get why he acted like he did. It's not really being cold, it's simply how practical exercises work.