Science says that Y chromosome means you’re a guy. Period.
Science is only relevant when it works in their favor.
You want to look up androgen insensitivity syndrome, SRY gene cross-overs, and non-functioning SRY.
Every now and then a XY individual physically develops as female. Or an XX as male.
This isn’t the case here - when the child was born, they looked at his genitalia and said “It’s a boy!”
But science finds some strange exceptions to the rule.