Rebdoniel, with all due respect – if you are kind enough to allow someone to use your home when you are not there (or even if you are), it is INDEED a violation of their trust, to enter rooms that are not permitted to you. Perhaps these Jews were already burned once or twice by people whom they trust and who likewise violated that trust. Nothing creepy about their locking their doors.
We were asked to host three bochurim for a Shabbaton in our neighborhood, as a favor to a local rebbie. Two of them were extremely ill-mannered and apparently brought up in a barn. But the worst part was when they invited SIX other boys into my home without our knowledge or permission. I heard noises while I was trying to nap on Shabbos, and came down to find these bar-mitzvah age boys jumping off my couch and playing ball with any handy objects in the room. I asked them why they were not at their program and told them to leave immediately. We never told the rebbie (we should have, we know, but didn’t want to get them in trouble), but I learned a valuable lesson.