My DS is 22 now, but when he had world book day - we could chose any book, he went as a Native American (known as red Indians when I grew up) and it didn't occur to us at all, that it could be offensive. He chose it as a nod to the Native Americans in Peter Pan.
Times have changed fast. He put up a photo off himself, in the costume, on social media, saying saying it was him culturally appropriating back in the day.
Scroll forward a dozen or so years and it occurred to me that, growing up in the 70's, we would play cowboys and Indians often and the Indians were the "baddies"- why?
The culture has come to fascinate me now, the tribes, their struggles and how they honour their culture now. They were not the baddies, they were defending themselves. It beyond bugs me that everyone grew up, thinking of them as in the wrong. I'm glad it is now recognised that they were in the right.
As for dressing up nowadays in the costume, I honestly don't know. When DS dressed up, it wasn't a diss, they look amazing in their tribal wear. If a girl dressed up as Pocahontas or Moana - surely it would be the same issue??