Friend’s boyfriend made a homophobic joke and she keeps insisting it was just a mistake..

Hey everyone,My friend has started dating a guy (they’re both straight) who asked her whilst they were on a date ‘do you ever feel nervous about a gay person coming into the public toilets when you’re there?’ She replied and said no.. how would you even know? And he said if they talk like this (does a camp voice). She mentioned it to me as she thought it was weird and I agreed and said it’s a bit homophobic. We’ve talked about it again since and she keeps insisting he was just joking and he just made a mistake and that I over reacted by saying it was a homophobic comment. Did I over react or is she under reacting?