We went to a Mexican restaurant not long after 9/11, and I observed this very thing. The host was no more Mexican than I am. He was Middle Eastern, and he was attempting to blend in with the large numbers of Mexicans who work in local restaurants. We've never been back to that restaurant, but I keep it in mind. What a way to have cover. Start a Mexican restaurant, and hire a bunch of illegals who won't give you away because they, too, will be in trouble. It's not a comforting thought.
Call the FBI.
How was the green chile? Did they use chicken instead of pork?
That would be the best clue.
On top of that there is no way the illegal Mexicans are going to rat out one of these Islamowhacks. Who would they tell....the INS?
They wouldn't even have to "swim" the border as some have suggested. Under NAFTA, trucks can drive all the way into the country, and NO they won't all be inspected. Remember these terrorists have money, unlike Mexicans.
This does not alarm me as I have noticed that it is very common for Koreans and other non-Japanese asians to open restaurants that serve Japanese food (teriyaki, yakisoba, etc.) They even decorate the restaurants with Japanese art, posters, maps of Japan, etc. It's merely a matter of marketing. Americans like and are used to Japanese food more than Korean food.
Similarly, it does not seem unreasonable to conclude that an Arab would make more money serving Mexican food that Arab food. I wasn't clear from your post if the host you mention was an owner. Even if he wasn't, I have eaten at ethnic restaurants where not all the servers were of matching ethnicity. BTW, how did you know that he was "Middle Eastern"?