He actually has a valid Mexican birth certificate, and the guys in charge of who is and isn't a citizen said he isn't.
They didn't randomly pick on this guy, and they've deported millions of people without deporting a citizen.
From what I've seen it looks like he has a birth certificate in both countries? If he does and his US birth certificate says he was born in the US then he is a US citizen.
> the guys in charge of who is and isn't a citizen said he isn't.
At least you recognize that who is and isn't a citizen is no longer determined by law and facts, but by "guys".