That's because you ain't facing a possible conviction depending on said definition...
I wonder how they decided who would drop the knife. Maybe, like a scene from “Police Story,” several were dropped, along with a few zip-guns. Sorry, unless there is video of every second of the takedown and arrest, I frankly would not trust any “found” knife near an arrested man. Just too easy. This is the city that invented the “nickel ride” now called “the rough ride.” A knife? Really? RKBA conservatives are now anti-”illegal knife?” And you have to parse legalities of springs and gravity etc to make it “illegal?” Sorry, I ain’t going down the “illegal knife” route. Anybody arrested can be “found” to be carrying something “illegal” in a world where cops drop knives. And if that offends you, sorry. That is the real world.