This is technically false. Only sins against the faith sever one's membership in the Church.
Pope Pius XII, Mystici Corporis:
While you're right, of course, I think what the anonymous poster meant was that there's no such thing as a "gay Catholic" in the sense we hear that term today (i.e. a "homosexualist" who formally supports the sod agenda, thereby formally denying Catholic teaching with respect to morality and Natural Law, and severing himself from the Church).
This notorious bundle of sticks springs immediately to mind as an example: