Now that the question has been answered…
One famous incident of this type was when one of the passengers booked on one of the Tenerife planes actually wanted to go to Tenerife (not Las Palmas, the original destination), so she simply didn’t get back on the plane when it was ready for the short hop to Las Palmas. Ended up saving her life (she would have been on the 747 where everyone died, not the other 747, where most died).
FWIW I was once flying home to Boston, when the plane had to divert to Providence due to icy runways in Boston. We did deplane, since they weren’t sure how they were going to get us to Boston anyway - the word “buses” was being thrown about. Since I didn’t have luggage, and my wife was going to pick me up anyway, I just called her and asked her to get me from the Providence airport, told the agent I wouldn’t need a new flight, and walked out. No issues, but it was my last flight of the trip so there was nothing left on the itinerary to cancel anyway. I’d assume I wasn’t the only person who made the same decision.
I was going to ask, what about clearing immigration. But on watching the video it seems he stayed in the airside part of the terminal because he was flying out of Joburg on another international flight the same day.
I dare say he would have had issues if he tried to go through immigration since he wouldn’t have been on the passenger manifest for any expected flight.
I had the opposite experience, in a way. I live in Boston and had to fly to California on short notice. I got a lower fare by booking a trip out of Providence. I boarded the flight, but after takeoff the flaps wouldn’t retract. You can’t make that flight with the flaps extended, so we diverted. To Boston.
As it turned out, the airline had another plane of the same model available in Boston. We parked at one gate, then the passengers walked off one plane, went a few gates down the terminal, and right onto another one. I got to California in time for the event I was attending.
I vaguely remember that that was my last trip on a 727. It was on United, and their entertainment system at the time had a channel to listen to the cockpit radio frequency. I was listening to that so I knew we were diverting about a minute before it was announced to the rest of the passengers.