Sadly, many students today try to attract attention and to disrupt class by shouting "he has a knife" - they seem to expect a SWAT team to come and evacuate the building when a pencil needs to be sharpened or a piece of rubber tubing needs to be cut.
I'm Language Arts so almost no reason to pull any knife during one of my classes. However, if I did and I got that response--especially as a jest trying to cause a disruption rather than actual alarm--I'd get pretty annoyed... Hat's off to you.