Glasses guy saw Ochaco after Izuku acted I reckon. She was under the rubble and was pretty far back. He only saw Izuku because he ran past him, and saw her when he was at a safe enough distance to actually look back.

I don't think that it's a given to save someone if it's a competition and you're meant to die trying, which may have been the rules for this type of exam. See Hunter X Hunter for the brutality that can go on during exams.