It happens more frequently than imagined...
I disagree with the post arguing that both sides were at fault (the OP for not bolting the door), but I immediately got into the habit of bolting the door even if I am going to be in the room for a few minutes after my own experience. I checked into the Amsterdam Marriott hotel many years ago, and was only in the room for a few minutes when another guest opens the door and wheels in his suitcase. I said, "Sorry, I was here first", and then always began bolting hotel doors!