You have good reason to feel that way. When there is only 1 spigot for a designated loop, or a designated section, no one should permanently hook up, no one!
You have 2 options. Report it to the campground host / or DNR / or campground manager.
Option 2. Unhook their water, get what you need and (if you want to be real nasty and send a message), leave them unhooked, hose laying on the ground.
If they happen to see you unhooking and give you a hard time, remind them it's a community spigot and no one can hook up permanently. If they still are belligerent, then definitely go no further. Report them to the campground management.
Bottom line, they are being rude simply do not care about anyone else. In that case, I'm not very pleasant in return!
Now .... If they run a hose, fill up their fresh water tank, then unhook the hose, I see no problem with that. I do that all the time in campgrounds (and many in Indiana have community spigots). No one ever says a word, in fact, I've even shared my hose with other campers to fill them up also, as usually, they don't bring enough hose themselves.
I always carry 200 feet of hose for just this purpose.
To answer your question, they are being very rude, and they are completely wrong if hooking up permanently! You have every right to take appropriate action!