I mean the same way Taco Bell is Mexican, Olive Garden is Italian, or any American Chinese food is Chinese. It's not "food from that area" but instead "food that reminds you of that area." That's how American culture works. People say America has no culture because everyone brings their own. Well, this is American culture, a bunch of food that's not from the places your family is from but food that might remind you of those places.

That said I personally would consider it Mexican-flavored American food along with Taco Bell, Taco Time, Taco Del Mar, etc. That said when I say "I feel like Mexican food tonight" I'm thinking of Mexican-flavored American food because you simply can't get Mexican Food in America as readily.