The head of security probably knows a simple pocket knife isn't a threat. I've known a lot of people who needed a screwdriver, scissors, etc that I've used my leatherman for and they have never cared or probably didn't even know it had a knife.

Years ago I was a simple pc repair guy and had to enter a correntional facility to fix the library pc. I emptied my pockets and the gaurd said you can't take that in, take it back to your car. So I picked up my pocket knife to take it back out and he said no, you can take that, you can't take the cell phone.