I am once again rereading YUTS and as I got through the sports festival I realized we never did find out if Aizawa noticed Mika leave. Did he notice before catching Izuku leaving her with Todoroki? And was he as thoroughly charmed by her as his students were?
I guess I’ll admit to that being a minor plot hole. I can’t really explain it myself. Maybe he saw her with AllMight and figured that Izuku was crowdsourcing his catsitting needs.
And Aizawa is always charmed by cats.