This is the thing I can’t understand, if he left the Airbnb and then realised he missed the bus and was thirsty, would be not got back to the house and ask could he get some water while he waited for the next one? Unless the house was too far from the bus stop to go back? Still not as far as walking back to Los Cristianos though? Or he left the bnb in not very good terms with the two men that he couldn’t go back?
If both Lucy and the witness who said he asked her about the bus are both telling the truth, then him going off road seems like a red herring, as why would he if he was lucid enough to call Lucy, send his location, tell her he had 1% battery, and the witness: he managed to ask her about the bus time and she mustn’t have seems too concerned after talking to him, why on earth would he decide to walk through the dry desert hills?