He had little notice, a surprise attack. The gun he used isn't recommended for killing anything larger than a human.
The shooter fired nine times but they haven't yet said how many times the grizzly was hit.
This is the handgun recommended for killing grizzlies and some government officials in Alaska are required to carry one, according to what an LEO posted on another board, $770, 2 1/2 lbs.:
http://www.gunblast.com/Ruger-SRHAlaskan454.htm
That's Ruger's website, go to it to see the recoil photos. A big, strong guy who is an expert and the revolver is pointing straight up after the shot.
A lot of us would be on our butt. That's exactly what happened to a fisherman who was surprised last summer up there. No warning, the grizzly was on the dead run toward him, spotted only 20 yards away. Two shots from the Ruger .454 Super Redhawk Casull and he was on his butt, but the grizzly died at his feet.
A post on another board also said those were the gun rules for the third of Denali NP that the shooter was in. Two-thirds of the park has a different status (??) and the gun rules are different there. Not sure if more or less restrictive.