Even if it were true that the bully didn't care about the sex of the victim per se, and only attacked her because of her popularity, the nature of what was done

Even if it were true that the bully didn't care about the sex of the victim per se, and only attacked her because of her popularity, the nature of what was done is still sexist. If I were to bash a competitor in public by reference to his homosexuality, it won't make anything better to know that I actually don't have any problem with gay people myself. It's unacceptable and downright evil.