@Susan10 Maybe he had something that he needed to store, like kitesurfing equipment, and it was easier for him to just keep your place. Maybe he just didn't want to pack up all his stuff. Maybe he thought he'd only be gone a day or two and it ended up taking longer.
I had a similar situation a couple of years ago with some American guests. They rented the place for a couple of weeks, and in the middle, they went to Quebec City, a destination that's a really long way from where my place is located. It so happened that I had to enter the unit while they were gone because of an electrical problem, and I found that there were about 40 cases of wine they had picked up locally and they just wanted a handy place to store it while they travelled around.
Personally, I wouldn't worry too much about it.