Well it does sound like he fell asleep. Lunch, sun, drone of prop, no one to talk to. Comes around and is coherent enough to get the aircraft back on the ground with appropriate assistance from ATC. I feel very sorry for him, His problem is that he may have failed one of the first rules in early aviation training, don't bulls**t your instructor, tell the truth. By labeling it as "I just blacked out", because the Docs can find no reason, he is unlikely to ever get a medical cat back again, or at any rate future airlines will not spend money on a known potential training risk. Had he said "I fell asleeo", it would have been an interview without tea and biscuits, being made to review the Human Factors, Performance and Limitations module of their study package 3 times over complete with exams and told he is on close supervision. It is probably end of career, one hopes not of course and whether it was a blackout or a sleep session he is a very lucky young man to have been straight and level, trimmed out with the auto pilot in.