@PawPadKnight I agree this is likely what happened. When she pushed him down, she didn't have time to "change" into cosplay before stopping him from leaving. It's either that his mind found some way to make sense of it, or it could be that he realized what was actually happening regarding her transformation and why she was avoiding him. I mean, they were talking in the middle of a crowd, and she clearly has issues with her appearance, so if he's not subconsciously denying her transformation and is actually really observant, then he simply made up the cosplay idea to protect her.
Honestly, I'd rather that he had figured it out and realized she was the Kaiju from the other day. That way, him covering for her shows how much he cares for her. If he was an asshole, he could easily call her a monster and get everyone nearby to gang up on her, and if he was just that dense, then their relationship doesn't really progress well at all.