They brought this upon themselves by considering a Gay-Straight Alliance group. They should have said NO immediately since it IS catholic and parents do send their children to Catholic Schools for a Catholic Education. He used a poor choice of words but should have had his say. And besides, he posted his comments on a non-school webpage.
If a CATHOLIC university goes after a student for making (crudely) the same point as does the teaching church while at the same time NOT affirming the Church's teaching, then it is pandering to a society that rejects virtually all the Church's teaching about sexual morality. The school thus says, See, we are not like THEM! "Them" meaning those unequivocally say that homosexuality is an immoral practice.