SlichosGenendel: As someone mentioned, maybe they knew you would open doors looking for your room, and didn’t want you looking in at all, even if you would never look in on purpose.
Who knows.
We lend out our house occasionally and my sister puts a sign on her door asking people not to go into her room- she gets a bit neurotic about it, especially when there are little kids who can mess stuff up. Unfortunately, it’s happened.
The bottom line it, it’s her right and it’s your host’s right. People have gotten burned.
We once came home after yom tov and discovered that we had cookie crumbs all over the bedrooms.
Sometimes you just want to contain the mess and not want to risk it.
The cheshbonos are complicated, and absolutely NONE of your business and not worth asking about on a forum like this.