Was this public or private land? If it is private land and you know this guy doesn't have permission then I would have left and called the police immediately. If this was on public land then I guess it depends on what the state law says. In Minnesota if the stand is up on public land then it is a public stand to be used by anyone. I would never use someone else's stand no matter what the case was but if you did leave your stand up on public property and the law says that anyone can use it then it is your own fault, but still a shady thing for another hunter to do.
I too have a question the cop that had someone's license suspended for "saying" that he owned your stand. Was this on public land? If so what crime did he commit? If this was your own private land then that guy should be on America's Dumbest criminals.