What about under “hostile intent”.
When hostile intent is present, the right exists to use proportional force, including armed force, in self-defense by all necessary means available to deter or neutralize the potential attacker or, if necessary, destroy the threat.
Evidence of hostile intent is considered to exist when a foreign force or terrorist is detected to maneuver into a weapon launch position; is preparing to fire, launch, or release weapons against US forces.
So according to the link you provided, 100% proof of a perceived threat is not necessary to use armed force, all that is necessary is for the enemy to appear to maneuver into weapon launch position, or to prepare to fire against US forces.
He didn't have to! Reaching into his pants to retrieve his weapon is the same as getting maneuvering into weapon launch position, or preparing to fire.