Why would anyone, even a Cop, be stupid enough to unholster a gun that's not a threat during a traffic stop?

A holstered firearm is not a threat to anyone's safety.

Officer body camera  footage of the incident is included in this video.

The officer who caused the discharge is a female.

Cops don't like it when people exercise their rights.  Look at HI's law that no rep from HPD had a problem with that all CCW holders have to let them know they're carrying and where the gun is located. But non-CCW holder doesn't have to do this.  And if a CCW holder doesn't do this, they will lose their 2a right in HI for 20 years as it's a firearm law that's broken, regardless if it's a felony or not.

Cops don't like it when people exercise their rights.  Look at HI's law that no rep from HPD had a problem with that all CCW holders have to let them know they're carrying and where the gun is located. But non-CCW holder doesn't have to do this.  And if a CCW holder doesn't do this, they will lose their 2a right in HI for 20 years as it's a firearm law that's broken, regardless if it's a felony or not.

if you're carrying an illegal concealed firearm, how can anyone require that you notify law enforcement when interacting?  Not only would that law be ignored too, you'd be trying to force the person to incriminate themself, a violation of the 5th amendment.

The penalty for the CCW holder is as you described which is just one more administrative law designed to strip citizens of their guns.

As for the video, the female officer was fired, and the department published a new policy that says officers are not to seize firearms from anyone unless that person is a prohibited person in possession of a firearm or is an imminent threat to the safety of themselves or others -- which should have been the policy in the first place.

Thats pretty bad, I hope he receives some nice compensation.

 If there was no reason to think he had committed any sort of crime they should have left him in his vehicle. If I feared he might pull their gun out in anger I would rather them be seated in their vehicle than outside their vehicle.

I missed it the first few times watching but the 3rd time I just happened to pause on the right frame and you can clearly see the officer's finger inside the trigger guard.