The cop was just stupid. He was a disservice to his force and to his community.
We just do not know this, for all we know you are right , but just as likely this policeman made the best choice he could have.
Here is a speculative possibility, for which I have insufficient evidence to have confidence.
A policeman sees a pair of jaywalkers, they look very young, but nothing really strange about them, they fit in to the neighborhood and don't seem to be armed.
The policeman pulls near then and turns on his lights intending to tell them not to jaywalk and to help them get across the traffic to safety.
What the policeman did not know was that these two were involved in a crime earlier in that day, and worse these guys did not know that the policeman did not know.
Was one of these guys a tough that was accustomed to punching his way out of trouble? this would be interesting to know , but we do not know .
Did the guy surprise the policeman as he was getting out of the car? That is a vulnerable moment if it is a surprise.
So possibly , the unarmed guy tried to get the gun right off the hip of the policeman and shoot him with it , a thing that happens now and then.
In the fight that happens over the gun , anything can happen, including both of them being shot.
The nature and severity of the injuries on the officer might not reveal the truth, but it could be that they would.
[][][][][][][][][][][][][][][][][][][][][][][][][]
...............cops are killed by their own weapons (51) Since 2000
This is roughly ten percent of policemen fatally shot in the line of duty.
http://www.thetruthaboutguns.com/2010/11/robert-farago/washington-post-more-cops-killed-by-their-own-gun-than-straw-purchases/