If the officers gun was a Glock it may not have a manual safety that operates as you describe.
Basically the gun has automatic safeties that prevent accidental discharges of the gun. However to fire, all you need to do is pull the trigger.
Another fact that is missing from us. What kind of gun was used and did it have a manual safety?
https://us.glock.com/en/learn/glock-pistols/safe-action-system
Do we even know what police department SS works for?
It’d be quite possible that someone in the LAPD would carry a Glock. No idea what the Corona PD has.
LAPD Equipment - Los Angeles Police Department