It was a regularly-scheduled DCL cruise last year, where DVC went in and booked a block of rooms for DVC'ers.
On board, they had several DVC activities - including a great group photo on Castaway Cay that was in one of our recent VM's.
Apparently the positive feedback from those who attended prompted them to try this "members only" cruise, this year... There was a LOT of interest in the cruise - much more than the rooms they booked could accomodate.
It was apparently a "quickly planned" event, as many of us didn't receive notice of the sailing until "after" the rooms had already been booked.