Well for one, that's not quite the case. You'll for example regularly see the king wear a fes hat when receiving foreign dignitaries, it's not quite like a Mexican sombrero.

Second, even if that was the case, I can assure you it's not unlikely for foreigners in Mexico to visit tourist-oriented places where you'll find locals wearing a sombrero. The fact that they're pandering to customers and this is part of a movie scene, doesn't mean the movie is the latin american equivalent of orientalist. The same goes for fes hats in Morocco. If anything, the scene exposes the orientalist nature of some of its characters who're ignorant and exaggerate the cultural differences, while others see the differences as quite ordinary and aren't fazed by them.