As a followup, it’s possible that the younger prophet was already in some rebellion against God when the older one caught up to him, for he was found under an oak. Although resting under shade trees is a tempting prospect, hardcore devotees would be leery about doing so even in observant areas because the areas were also public restrooms and may have been easily defiled – moreso if Gentiles had possibly been camping and/or pooping there! This applies to trees near a road, btw, not to trees well back from a road. Although even then you’d want to be careful your hair didn’t get caught in low-hanging branches (since those who hang from a tree are cursed per Torah). Worse, in a time and place like Bethel-of-Samaria where this is happening, pagan sacrifices were being made under trees whether near the road or not.
The younger prophet couldn’t have gotten far out of Bethel already, and he’s already resting under an oak tree apparently near the road. For us that wouldn’t have been a big deal, and after all he must have been starving and dehydrated. By the principles of hard kosher Torah observance, though, he shouldn’t have been caught dead under that tree! – nor gone near it even for shade, considering the stringency of the terms of his self-sacrificial mission, where he would only survive by a miracle from God: not drinking for three days on a round trip of four to six days. The command not to go back the same way, means it would be impossible to take the shortest route both coming and returning. (The area wasn’t a desert yet like today, but dehydration is still dehydration.)