From a still frame of the video, it looks like the taser is a 7 CQ. I believe that particular taser only carries 2 shots.
If 2 shots were already fired, the cop had no reason to be all that worried about it. If the cop was in fear for his life, he could have just stood up and backed away. If the guy runs at you, take him out. If he runs away, waive good-bye and call it in on the radio. Again - it was a traffic stop over a license plate.
As so many of these go - both the victim and the cop have fault. One - STOP FUCKING RESISTING. And for the cop - de-escalation is a practice completely absent from just about all of these shootings.
Again - that's IF the taser was empty of usable rounds.