He was below tree line, I'm guessing 7,000' or so.. hard to say what the temps were, but DA wasn't the issue so much as his poor decision making.
Sparky Imeson in the "Mountain Flying Bible" repeatedly warns you never fly beyond the point of no return, that's where you can always make a 180 glide back toward lower terrain.
This guy boxed himself in at low altitude. From the grainy video it seemed like he would've had more room to maneuver if he would've turned right for a moment to hug that ridge line, then did his tight turn to the left... it looked like there was a bit of a bowl at the base of that rock face which would've been plenty large enough for a 180-turn... but instead he turned right into rising terrain, once there panic set in and he tried to keep the nose away from those scary tree tops and the extra load factor in the bank pushed him over the edge. The airplane was trying to help him, as most Cessna's do, by dropping the nose but he persisted and mushed it right on in.
One thing that happens in the mountains is you often loose a good horizon reference, because you're looking at lots of different mountain face angles instead of a nice horizon, so it's possible he was already in a nose high, low airspeed, going up that canyon when he thought he was in a normal cruise attitude.... hard to say... but he put himself in that position.