On the other hand, if he's in significant danger and he doesn't draw his weapon, he at further risk of harm if he can't draw the weapon in time.
LTC8K6 pointed to a distance of 15 feet where an individual can reach an officer before they have time to draw and aim their weapon. Assuming you trust his claim, that's not very far, and from the description in the opening post the incident started with the people in close proximity.
The officer can't at that point engage hand to hand without risking the loss of the weapon, and s/he can't use any nonlethal alternative like a baton, stun gun, taser, or pepper spray.
Since I didn't witness it, I couldn't say for sure that pulling the gun was excessive...but in the absence of a weapon in the hand of the suspect, and assuming that there was no immediate threat to others, the officer should have had training...