Mestizo meaning Spaniard and Azteca or other indigenous ancestry of course. It really bothers me my girlfriends brother is like this (she's latina from Cuba). Plays up the Spaniard and Aztec part of his heritage and denigrates blacks and Asians.
Yes he looks like a 4chan user
anglo countries conceive of race from a '1-drop' premise, you're White or Not.
Spanish, French, and Portuguese colonies did not and had in-between castes. it's not disqualifying to have mixed ancestry and 'be' white---the descendants of aztec nobility are for instance considered white. which incidentally fits with your example somewhat, though i expect he's not a marquess or something.
which is to say a lot of these people do not recognize the KKKrakkka definition of them as non-white, they consider themselves white. and the reason they won't abandon this is like every potential victim of fascism's reason for supporting the right; their real or imagined economic affiliation with the capitalists.