It's possible that the restaurant is one of those "dual cuisine" establishments that features the cuisine of both nations. Sometimes it's the owners who hail from the two different country, or maybe a chef who is adept in both cuisines.

When I lived in the Bay Area, we used to go to a husband/wife owned restautant in San Francisco that featured both Mexican and Salvadorean food. The wife was from Mexico and shared the kitchen with her Salvadorean mother in law (the husband ran the front of the house). OMG, the pupusas were to die for