Aizawa just seemed to let Momo run in the opposite direction. She managed to get to Todoroki faster than him, and even freed him before he arrived.
He should have more experience in catching up with a girl in a skimpy suit.
Momo had zero confidence after the sports festival and todoroki was known to go solo for most of it and not rely on others, which is why Aizawa chose to fix those problems/weaknesses instead of outright crushing them (and breaking the rules a little for what this exam was meant to be for). What he did was important for the long term for their development as future heroes.