I think the cops did right, nowhere does it say the guy hit the ground. The cops showed up asked him to put the gun gun down and lie down, they cuffed and searched him upon realisation that it was a pellet rifle and after checking that he wasn't breaking any laws they probably released the guy. The cops all have their guns holstered. No one seems to be yelling.
They saw a guy with a gun disarmed him checked if everything was ok and released him, I don't see anything wrong here. If I was a cop and I would have seen someone riding a bike with a rifle coming out of a backpac I would have arrested him until I was sure the only thing he had on him was a pellet gun.

It could have been avoided if he had transported the gun in a case or bag.