I think the cause would enter into it. I mean, if a fire started because there was a fault in the hotel wiring, that's certainly something that can be argued in court.
It could be but is that really where you want to be? The UMC owner manual has a warning not to use extension cords and finding yourself fighting a big insurance company attorney is probably not fun.
I agree that the OP was on the receiving end of an attitude he didn't deserve, but I still think that there's a huge risk in plugging in like that without permission.