It was an overreaction on the part of the professor, presumably stimulated by the frequency of school shootings in the past decade. In the wake of Columbine and Virginia Tech, schools have become much more cautious with anything that even hints at the possibility of leading to a shooting. Imagine if the teacher hadn't investigated and the student had ended up being a wacko and shooting up the school; her ass would be up shit creek without a paddle for not reporting it "suspicious" that he would give speeches about guns. It's an unfortunate pussification of America in the wake of horrible tragedies, and I don't support it, but I can see why the professor acted as she did.