Bbm
Yes this seems the most plausible explanation. Trailhead sign sent to GF at 9.20am.
What confused me was the sign said Asforiditis 2 hours and created a bit of confusion in my mind as to when he started his hike.
The back of 7am seems way more likely to be the starting time. I am still of the mind that he is in the Steki Tou Machera area.
A poster had mentioned upthread, can't remember which, that drinking Coke in hot weather can create stomach problems. Not sure how accurate that is but perhaps could offer an explanation to what happened.
IMO
I assume the Coke would be chilled otherwise it would be undrinkable at 100F. It has sugar and caffeine. A quick cold pick-me-up for a hot hike. I also assume he ate something for breakfast and had some coffee, too, so it wasn't as though this was all on an empty stomach.
Whatever happened, was after he left that place and was so sudden he didn't have time to make a phone call, hit an emergency button, run or walk back to the Steki place, and didn't cause him to drop anything or leave any sign of a struggle, a fall, a note, drop his pack, make a signal cairn or use a rescue whistle, mirror, or a fire. The very short comment about the interaction with Sophia does not sound as though she thought he was in distress, looked ill, or was not making any sense. The mention does not indicate she thought there was anything wrong with him.
It is, indeed, as if he tumbled off a cliff or wandered deliriously into a ravine.