Nationality Stereotypes - But we're speaking Japanese!　日本語喋ってるんだけど

I'm impressed. Their japanese was impeccable. Video was funny, too.

It's actually fairly common in Asian countries because unlike you Western countries, most Asian countries don't have a lot of immigrants, and thus the large majority of the population would be Asian. People conclude that most non-Asians are visitors.

Asian countries also emphasize foreign language heavily so most people know how to speak basic English.