Most Mexicans don't speak their native language. Spanish is the language of the people who colonized them and that they altered forced to adopt. It's more accurate to say they speak Spanish imo. Otherwise, that's like saying Cherokee Native Americans, when speaking English, are speaking "Cherokee" just because they may have some slang that other English speakers don't have. And no, they aren't speaking "Cherokee," that language was forcibly removed from their culture just like many native languages were removed by the Spanish and to a lesser extent, the Portuguese.