Studying this and other bear attacks its clear that for bear attacks where injuries are incurred, the time between recognizing the threat and the attack was less than 3 seconds. My understanding is that he was getting water from a melt-water stream. Unless he has three hands, two to collect water and one to hold the gun, and three eyeballs, one for what his two hands are doing and two for binocular vision to correctly gauge distance and position, I don't see how a gun would have helped here. In fact the two eyeballs would have to be in the side or back of his head. (And maybe extra brains to do two things at once). 

Bottom line is if you are solo, a gun or a bear spray is a false sense of security. You have no security. Even with two people, a gun would be difficult to use effectively entangled with your buddy "in dense brush". 

Making a lot of noise is just something people feel ridiculous doing, as far as I can tell, but I think it might have helped.