Yea AFAIK the whole "bullet gun fingerprint" idea is total bunk. You cannot tell if a specific bullet was fired from a specific gun.
Note the distinct absence of any evidence that protesters fired at police. The police have access to hundreds of cameras at the scene, from bodycams to professional videographers on police payroll, to drones and aircraft.
If there was evidence that protesters fired at police, you can bet the police would be publishing it.
Decent probability this was friendly fire.