Maybe we're thinking of two different definitions of the word sexualize. I'm going with to view or treat primarily as an object of sexual desire. I don't think he's doing that to his mother. His friends probably are, and his offense would be feeding into their sexualization of his mother not actually sexualizing her himself.
It's not a big deal one way or the other. I just get wary when people apply these terms too generally because sometimes we get to a point where basic human behavior gets treated like an offense.
