Simply read the article and it immediately became apparent from what was written concerning the actions of the protector how it could have went completely wrong. That said I would really like to know why I shouldn't comment are you my superior, isn't this a platform where one can share thoughts, no? Care to share why you even responded at all as you added nothing to the discussion, or was it just a lame attempt to bust the chops of a new member?
My initial thoughts are similar to what Mac66 stated above, exposing his weapon was his biggest mistake on many levels as he doesn't know whom is around and who may confuse him for being an assailant. What if there were other assailants that hadn't yet joined into the party and just standing by waiting to see what unfolds and they see this guy with his pistol at the ready.
I recall a similar incident in a Walmart several years ago where the hero ends up getting shot in the back after he drew his ccw because he didn't know there was actually more than one perp involved in that incident. I recall it was a girl that walks right up behind the hero as his attention was drawn towards the shooting and shooter, as the hero gets ready to respond, the girl drops him from behind.
You don't know what you don't know. In fact, you will never know what you don’t know. There will always be gaps in your knowledge, places where you are absolutely clueless as to your ignorance.