Perhaps a bit of silver crossed the camp host's palm. Wouldn't be the first time for that sort of thing. ;) But really there are a number of possible reasons. It's too bad it didn't work out better for you on this occasion.
If one were to call the main FS office, my guess is they'd say the camp host has discretion, and they support his decision.
Camp hosts and park employees have a tough job sometimes, trying to keep everyone happy. I recall one time I pulled into a state park where I had a reservation, went to the campsite and found it occupied. The people were gone sightseeing for the whole day, a relative made the reservations for them and due to miscommunication they thought they had that site for 2 more nights. No way for them to hustle back and pull out, and the CG was fully booked, so the folks at the check-in office gave me an unofficial 'campsite' that was nicer than most of the regular campsites, a spot with a fire ring (but no electric) they kept open for emergencies. They even offered me free firewood and ice to make up for the inconvenience!
