Agreed. Without knowing their details, it's hard to know what they faced. There are definitely seasonal differences in availability that go well beyond the traditional holiday peaks.
I've now fallen into the, 'If you might go, book it!' category. The small, fully-refundable, deposit on a room only reservation makes it relatively easy to hold your spot in anticipation of a likely stay. The moment we decided to come down this past summer, I booked a site. In the end, we used our DVC points and cancelled the Fort, but I knew I had it just in case. If you have to cancel, cancel, but it's a lot easier to adjust by a day or two when things become clear than it is to try to cobble a stay together later on.