I agree that Doloff's move appears to be a defensive block which caused Keltner to smack the ugly off of him.
"Normally", that would cause both combatants to back up. It should have ended right there, and probably would have if Doloff had any real security training.
That's a long way from use of a firearm. Lots of intermediate steps available.
Interestingly, that's exactly what Keltner did. He started backing up, and was backing away as Doloff drew and fired his gun. (In fact, this sequence is so blatantly obvious from available evidence that the Denver Compost had to describe it as Keltner "backing up to use his pepper spray." (Because everyone knows that you back away in order to deploy pepper spray. )