Having a Katana like handle sticking out of your backpack is not even in the same ballpark as malicious provocation. Yelling "fire" in a movie theater? Please.
Having the cops check out a guy with a sword is not 'chronic distrust of anything and everything'. It's a prudent move that is standard operating procedure around the world.
On top of that, this appears to have been at a school where there was a violent incident with a freaking samurai sword not so long ago. How can you reasonably maintain a position that in those circumstances it's irrational to go look for the reported sword carrying person?
People's judgments of situations are influenced by their previous experiences. Is a fear of flying of someone who survived a plane crash rational? No. Is it normal? Yes. Is a (heightened) fear of dark alleys normal for someone who was raped in one? No. Is it normal? Yes. So, when someone walks in an area where there was recently an attack with a sword, it's perfectly normal for people to be more jittery than they would have been had there not been a recent attack.
Apart from this, there is a different dynamic at work. After an attack, there is public pressure on the people in charge to make the area more secure. We can bicker about the measures they take and how it's token security blah blah blah - but when you get a signal that there is a guy walking around with a sword, as a security officer you'll run your ass off to get there and check this guy out, before it's another nut job who has come to vent his frustrations on his ex roommates or whatever. Rational? Not sure, may not - but irrelevant. Is it understandable? Yes.
You can argue now that you feel that these reactions are wrong because they are not rational (for a narrow definition of rational, i.e. based on facts and pure, logically sound reason). That's fine. However for you to not acknowledge that the reactions as they were in the present case (for as far as we know the facts from this thread) could not have been foreseen, or that they would come as a surprise, or even that they are not 'normal' reactions for the majority of the population, is plain intellectually dishonest.
I am not a criminology expert, so could not reliably say how much of an increase it would be. But it would probably be enough to justify unusually strict enforcing of an existing rule barring weapons on campus.
If someone called in a regular old umbrella as a weapon, sure, I'd call that paranoia - but this thing is designed to look like a weapon, and you're blaming people for thinking it was real?
"Handlebar fashioned specifically to look like katana assumed to be a katana" - is this really so unreasonable?