I was in law enforcement for many years. I had to qualify at the range with my weapon every quarter. When we shot, it was one round to the head, and two to the center of mass. They said that if we ever got into a shooting situation, we would revert back to that training. One to the head, two to the center of mass.
I'm not sure how that sherriff was trained, but I believe that for the actual act of shooting, he was probably reverting to his training. I also think that he got hyped up during the pursuit and had too much adrenaline coursing through his veins. It clouded his judgment. The shooting should never have happened.
I think he was scared to death. He was no more than 6ft away from the airman and shot once in the shoulder, chest and thigh.
Either that or his gun got away from him.