The bear obviously was underweight and old. Its getting colder, and it was charging the man full speed. I would have to deduce that the bear was after the man. The reason does not matter but I know that bears are opportunistic. They will eat humans if starving and if its an easy kill.
The man was smart carrying the sidearm. No doubt about that.
This happening has made me feel very stupid about carrying bear spray while in the Rockies/Wasatch/Tetons.... I will be in the market for a 454 real soon.... Or, is there anything else I could hip carry?