I doubt if he had a heavy coat with him. The sheriff said that after seeing the photos, he was even more worried about their ability to survive, because they were lightly equipped. I take that to mean he could see what kinds of jackets, etc., they were wearing. Plus, James was found with no insulating-type jacket, just a waterproof jacket. So my uneducated guess is they were dressing light, as they were planning on a quick ascent and decent. When you are physically active, you don't need many warm layers. That's my guess.
Here is a link to the most up to date info.
http://www.summitpost.org/album/252008/mt-hood-rescue-overview.html
See, that doesn't work for me...even a perfect day up there has to be in the teens, and probably below zero. we're talking 10300ft, that is positively polar.
When working, I can see being in a light jacket (better not to sweat), but the minute one is still, like when on belay, or whil waiting on point, or even just at rest stops... The minute one would stop moving, one would get cold REALLY fast.
Lightly equipped would include layered personal warm-wear by necessity. It might preclude a bivybag, stove, less rope, etc...
-Bruce