I'm sorry, but I'm not so sure about that. My SIL just had a knee replacement and has found that going up her stairs is much less painful than coming down. I've never had a knee injury, so I can't say personally, but perhaps it makes a difference as to the type of knee injury? Anyway, I found this which seems to support what my SIL has described:
Does your knee hurt going downstairs? - Physiotherapy Works
I don't like the fact that his friend left him either, but I haven't heard enough of the circumstances to accuse him of hiding something. It doesn't sound like there was any foul play involved, although they don't say. Hopefully, we'll hear more tomorrow.
Incidentally, I grew up near Mt. Hood and spent a lot of time at Timberline and other nearby ski areas, lakes, etc. It is a very rugged terrain and these trails include steep inclines, drop-offs, and areas where you have to cross water. It sounds like he made it to the 37-mile mark where the Timberline Trail meets the Pacific Crest Trail and may have headed back to the Eastern Fork to set up his tent. ?
Timberline Trail around Mount Hood Hike - Hiking in Portland, Oregon and Washington
I may age myself a bit, but have you ever seen the movie
The Shining with Jack Nicholson? It was filmed at Timberline Lodge. Just a bit of trivia...
There are beautiful views from the lodge and it's a popular wedding venue.
https://.timberlinelodge.com/mountain/summer-activities#pct
MOO