It depends: did the guy dress fancy? If no then there was not much of a real problem at all, but still bad decision making
Did the guy dressed fancy, but wanted her to dress down?
If the latter one, Congrats it’s either a narcissist or someone with a big ego trying to get an ego boost and by embarrassing her. As far as I’m seeing she also mentioned that she kind of felt embarrassed so i assume it’s very likely the case that it was a narcissist or someone with a big ego she got invited from
conclusion: the girl was right either way, the guy on the other hand bad decision making, narcissist or big ego