Meh, I get your point but it's an extremely murky water to place labels on people's cultural knowledge, who deserves to serve as an authority and who doesn't. I'm a Finn who's lived in Finland all her life, so I consider myself more an authority on Finnish culture than say, a Finnish-Canadian teen who doesn't speak the language much but spends most of their summers here.

And yet, a Welsh man who's worked and lived here, married to a Finn for decades, probably has considerable cultural knowledge over the Finnish-Canadian because even if he's not native, he's "Finnishized" over the years.

Put it another way: would I let the Welsh man or the Finnish-Canadian teen lecture me about my own culture? No. But would I consider them better sources for cultural knowledge than an American editor who just has Google at their disposal? Yes. Even with stuff where knowledge varies and there's no true answer (like customs, which may vary from area to area, from family to family), there is a point where somebody's authority on their own culture shouldn't be questioned.

And of course, sometimes if somebody is really offended, it's best just to apologise.