If he did that today it would be called "cultural appropriation" and his reputation would be trashed. But thankfully he did it years ago so we've still got a chance to hear this sort of rare music.
Okay, but he was, so.... this comment is pretty empty. And even if he wasn't, he made this music in collaboration with First Nations musicians. I don't think there's a taboo against people working with each other who aren't of the same ethnic background. Cultural appropriation accusations usually come up when someone who has nothing to do with a certain ethnic background starts drawing on it for something - and even then those accusations are often pretty empty.