If a disability student group was working with a student activity group in screening a film critiquing the conservative movement for its view of people with disabilities and the Republican student group pitched a fit about it and as a result the disability group couldn't air its film-that is a form of bullying, because now in its place the Republicans only wanted to inject themselves into the conversation without giving fair audience to the disability group.
That's the difference. Had they aired the film and then put in a moderated discussion or the like, that would not infringe on the Expression of the group's that wanted American Sniper to be shown. Instead you cut down on the ability to watch the film in favor of then allowing people to attack it. It's a power imbalance pure and simple.
It's antithetical to the purpose of the university.