The guy has a drill in the seat next to him. He throws on the breaks and the drill slides onto the floorboard, possibly under the break pedal. He reaches down to move it because it is a hazard to have something sliding around under the break pedal.
However, if you have been on the force for 14 years and driving for 20 you would know that this is happens often to vehicles that are stopped suddenly and you wouldn't be shooting drivers for pushing things back under the seat.
And then there is the matter of ballistics. If his hands are both on the steering wheel, a shot to the abdomen from the passenger side window where the officer was is easy. But if he is reaching under the seat as the officer claims, the shot would have likely hit his arm or side -- not his abdomen.