Great, interesting comments from everyone. Thank you!
And, my guess, at the time, was a "hand washing" issue. No way to know for sure, ever, though.
His decision making had obviously begun to deteriorate, too. He made a series of decisions in the 48-72 hours before we found him that, with hindsight, I think he'd have done differently. He would have suffered less and increased his chances of rescue and/or self extraction greatly by doing a few things differently. Like, for instance, the last decision he made, which was to leave a parking area next to a Jeep trail with picnic tables and a pit toilet, when he didn't have the strength to make it 700 yards before collapsing. Or, as just mentioned, staying by the potholes he had found the night before. There were other decisions made before these that all kind of piled up on him. And, I should note, my impression of him was that he was actually a very intelligent young man.
But I think it is pretty normal for most people in that kind of condition and that much stress to start making poor choices though. Very intelligent people included. And, for me, that's the really important lesson to take home from this - when you find your tail in a crack (and I have...) - slow down and THINK. The kids and I have had several discussions about this already and that is the theme I'm trying to drive home to them.