Apparently, you've never heard of Airsoft guns. They shoot mostly harmless small plastic balls. The main threat is eye injury ("you'll put somebody's eye out!").
This is police state overreaction on parade. If the kid didn't point it at anyone, they had no reason to shoot-- even if it was a real rifle.
My brothers and I had a pellet gun with a telescopic sight back in the 60’s.
We could kill pigeons at 200 feet, and break bottles at 100 feet.
This is a tragic death.
But I disagree about overreaction.
There are violent Hispanic gangs in Santa Rosa, the gun clearly resembles an AK-47, the photo I saw looks like it has a metal barrel and a metal magazine, the young man did not respond to two shouted police commands, and he turned himself and the weapon in the direction of police officers.
An instantaneous decision was necessary.