Of course not, I have many Mexican friends who have fair hair, are Jewish, have
blue or green eyes, etc. That has nothing to do with it.
If he was born in Mexico, then he is by definition a Mexican citizen, according to Mexican law — this is what happened with my daughter.
I’m just pointing out that being born in Mexico does necessarily make someone a Mexican-American (or Latino or Hispanic). Millions of American babies are born to American parents all over the world every year, and aren’t considered to be hyphenated Americans just because of their place of birth.
Having Mexican heritage or ancestry is the key component in being a Mexican-American, IMO, not place of birth, skin color, eye color, hair color, last name, religion, etc.