Not enough details. Article makes it sound like the clerk was a bit sloppy, but security cam would show if he was in fear of life or not. In either case, sounds like he did society a favor.
Never had anyone point a gun at me, but there’s a very distinct side of me that would believe that my life was in danger so long as that person was still alive and had a gun in their hand. Perhaps because it would be. It wouldn’t ‘turn-off’ the moment they turned to (possibly/likely) leave the store. Shifting from survival mode in a deadly confrontation to “Oh, OK, everything’s alright now; no threat” would take me quite a bit longer than a split second.