They're just Mexicans. They aren't a mixture of South and Central American ethnicities; all the others are about 5% of the total.
Just Mexicans, doing the parasite play they did to the Toltecs and the Spaniards: living on the fringes, surviving on scraps, waiting for the day they can overrun and collapse the better civilizations they simply can't conceive of or create.
I was simply quoting the demographic page from the small town I grew up in.