Regarding cell data, was he using a local cell phone plan?
Interesting!
Wearing all black in the hot sun is not the best option, my understanding is that white is best for keeping cool.
The photo from the linked ABCnews video - is that a recent photo from his current vacation?
What do we know about his travel plans? When did he arrive, when was he leaving, where was he going next? Was he traveling with anyone, meeting up with anyone?
Was he staying at his home, airbnb, shared home, hostel?
Did he ever take a small fishing or local boat between points on the Island?
Is there cab service between Lagada and Kalapola? There must be a bus.
The video of him putting his things in his car - not clear, but if he has a car, and all his things are in the car, why is he hiking to Kalapola to meet someone for lunch? It's a 4 hour walk there, 4 hour walk back - or take the bus on a hot afternoon. Why not drive for the lunch meeting, take a shorter hike earlier in the day, or in the evening?
He stopped to buy water - must have been extra thirsty, since it is believed that an experienced hiker would have lots of water for the 4 hour hike in 96°F weather.