I can’t imagine a cop telling someone to reach for his gun, but who knows. And considering his military background, he had to understand he was considered a threat until the legality of his CCW was confirmed.
All three were probably trigger happy and ready to go so when he followed the instructions of the first one to drop his weapon, the other who was screaming "get your f___ing hands where I can see them!" opened fire. Hearing that initial shot, it is likely the other two quickly joined in.