When I was in college there was a group that went by the name of "Environmental Fundamentalist". They were extremely anti government, anti usa, and supported and justified at the time, the killing of US troops in Iraq. They were extremely vocal, and too be honest it scared me. The final straw was when the chairman of the group told me, "I think everyone of us has a person deep down inside of us that is willing to strap an IED to his chest and blow him self up".
At the time I was doing an internship with Connecticut's Department of Emergency Management and Homeland Security.
I alerted my boss about it, and proper action was taken.
Sure it is their right to say that crap, but I don't see myself at all different from the girl who reported this to the police. Sure, my case is a lot more extreme, but guns are a very sensitive subject to some people, especially on campus following Virginia Tech, and I see no problem with her reporting what she thought she saw....Reporting something could mean the difference between two different situations, 1 which could end with a very chitty outcome.
That said, I also don't think it would be to bad for this girl to try and contact the guy she reported and tell him it's nothing personal, she thought she saw a threat and acted accordingly, and hope he understands.