As hosts, we would have gone and talked to the people who moved in and notified them they would have to move. If they were not cooperative, we would then have called a ranger or the LEO. In the places we have been, they would have made them leave so that the person who "first" paid for the site and left their tag on the post was allowed to occupy the site. We have never been someplace where no action would be taken. You did take the high road, but I sure would have been ticked. We do often see people with no toad or a b or c class rv leave a chair or something on the site when they leave. There usually is not a problem though.