NOTE: This is almost all speculative, just wool-gathering.
Having a sidearm on one’s person (CCW or Open Carry) does not necessarily imply competence in self-defense. It may be an indicator of the possibility of competence, but as numerous supposedly capable law enFARCEment ossifers have demonstrated over just the past few years, it’s not dispositive.
Many factors determine self-defense competence: proper practice (in two meanings of “practice” *heh*), attitude, situational awareness, physical limitations–both personal and situational. The one true First Responder in the Umpqua Community College Social Darwinism Experiment was unarmed, save for his own body and mind. Did he throw a chair or desk at the attacker in preparation for his own physical attack? So far, no one has said. Did he even have a knife on his person? Apparently not.
Do note: the general “21-foot rule” on knife attacks would not have directly applied here. It was “clinically-established” in casual experimentation 30-some-odd years ago with a specific set of restricted parameters: trained law enforcement officers with firearm holstered were consistently unable to effectively engage an attacker armed with a (mock) knife before being “stabbed” if the attacker was within 21 (or variously, 22) feet. Simulated wounds received by the officers ranged from debilitating to deadly.
Of course, this demonstration did not just use officers who were supposedly trained in the use of their firearms and regs on the use of deadly force but a trained “attacker” as well. Had the former Army guy who was the real First Responder been trained in responding to an armed attacker, even though unarmed, things might have turned out a little different. Had he thrown one or more objects that could cause real harm to the attacker, things might have been different.
Do note that I greatly admire the courage and determination displayed. But it still, at least partially, came down to proper practice, attitude (OUTSTANDING!), situational awareness (?), and physical limitations–both personal and situational (particularly: he had already been targeted when he decided to act; he apparently didn’t even have a knife on his person).