“The guy he shot was unarmed and wasn’t going for any weapon...”
You don’t know that in the moment. Guy had apparently already been physically aggressive, that starts the clock.
He was shot because he threw popcorn. Period. Nothing noted he was reaching for a weapon. It was a standard reaction to someone telling him to stop texting which in itself is quiet. He threw the popcorn at a moron who then over reacted and shot him. Police protect their own, retired or not.