I only have what's posted here to know what happened so I'll just tell you what I've done in the past.
First I don't shoot anyone the finger for any reason. I don't yell or curse anyone when diving.
What would I do;
'Hello, 9-1-1, I'm an off duty Deputy Constable I'm headed *** bound on *****street. I'm following a vehicle and driver who are driving erratically.'
'Yes, I will stay on the phone and give you direction of travel as your Officers approach.'
When the locals arrive, let them handle it. I will tell them my version of what happened.
I have arrested several people while I was off duty, shop lifters mostly, but I never chased anyone in my vehicle. I will follow someone as long as it's safe to do so, at the legal speed limit. If they stop and exit the vehicle I drive down the street until Local LEO arrive. I figure that if they've parked the vehicle they are no longer in Road Rage. I will not confront someone unless it's apparent that they are about to attack or injure someone.
I some shoots me the finger I just wave and slow down to let them get ahead of me. My moral duty is not to make a situation worse.
This is Me and what I've done in the past. This is not to judge any other LEO's actions.