So if I'm not Mexican I can't celebrate Cinco de Mayo? Or did I misunderstand that post about your uncle?
put very simply, and from somebody who is definitely white and still learning about these things as well - cinco de mayo is a mexican holiday to celebrate mexico’s victory over the french on may 5, 1862 in the battle of puebla. now in america the holiday has genuinely taken on a different tone and is generally meant to be a celebration of mexican-american heritage and culture.
the problem is that people (GENERALLY white people, sometimes others) take the day and completely twist it around until the holiday has no meaning rooted in mexican culture at all - and they use it just as an excuse to party ( ””fiesta”” ), get drunk, eat lots of taco bell or chipotle, have fun, etc. now, there’s no problem with having fun and letting loose - but when people are doing so at the expense of a part of somebody else’s culture, they are appropriating that culture and erasing that heritage. ESPECIALLY when the celebrations non-mexican people have aren’t really celebrating that culture at all, and usually are making a mockery of it or celebrating using stereotypes. which, really, isn’t a cinco de mayo celebration at all.