I know I'm late to the party, but the First Amendment does apply to public universities, and I am assuming California University is one, since they're invoking the First Amendment. So, since the student event is tied up with quasi-government funding/hosting, it does become an issue if you try to ban a speaker on the basis of content or viewpoint. A governmental entity can place reasonable time/place/manner restrictions on an event (so, if there's a security issue, they could move it), but they have to be content- and viewpoint-neutral.