The Mexicans may think he was discriminating against them as most of them don't speak correct Spanish. The Cubans speak correct Spanish but not the Mexicans.
I was in a situation in Las Vegas a few years ago and some Cubans were speaking Spanish. My Mexican American friend who speaks fluent Spanish could not understand them. My friend then explained the difference in the language.
I don't know what Mexicans you are talking about that don't speak spanish. The ones I know in Texas speak spanish just fine. Don't lump all Mexicans together.