It's not IDB as they seem to be covered by the CoCs here. Where they screwed the pooch, so to speak, on this was in not making it clear to the OP (and I'm assuming that they didn't send or convey adequate information to this effect else the original rant would be totally off-base) that the "reservation" was still subject to first-come-first-served rules. This should have been made clear before the trip started. Yes, it does seem to be in the "fine print," but there's a reasonable expectation that a reservation actually reserves something.

Cheers.