You aren’t OP and the original comment you replied to was not addressing you. Dress how you want.
The point is fair, if you want to fit in at any event, because you do in fact care, then it helps to dress in a manner that suits the general style of that event.
If you don’t care, wear what you want. I’m not sure why you are getting offended by something so trivial that was not directed at you.
It’s how human nature works, before you meet sometime, all you can judge them on is their appearance. Are they wearing a filthy beard and rags at a concert? Probably a crazy hobo. Are they past middle age and wearing a mankini? Probably a big borat fan and a bit of a weirdo.
It’s not a difficult concept and you don’t have to care if you don’t want to. It’s all good.