That is totally absurd. Next time you have an asshole cop say that to you just casually look at your surroundings and then point out the improvised weapons you see: rocks, glass bottles, sticks, etc. and focus on any of the ones that can kill more effectively than your pocket knife.
People kill people.
If I didn’t have 12 members of my extended family with me, including grandkids, I likely would have made an issue of it.
Sadly, the cops don’t care about violating your constitutional rights. They have a job to do and the violators will need to argue constitutional rights in court.
AAMOF, that exactly what they will say, “You’ll have to tell it to the judge.”