Here's another link with a bit more info and a video interview with him,

Fish&Game said the pack wasn't torn up, but there is blood on it. They're going to test it.

Those blood test should tell us something. If it's all his blood, I'd have to wonder if he just got too close to that bear or the cub and got smacked around in the process. The cuts on his arm don't quite fit in with the rest of the story, but the old fart sure is sticking to his story and he doesn't seem a bit concerned about what others think of it.

Personally, I think it's all quite plausible. Strange things do happen. In the link BZH posted there were some videos of interaction between bears and cougars in the wild. They are really quite interesting and surprising.