Disney seems to be under the impression there is a lot of expansion room at DCA. Remember last year during the gate tax drama with Anaheim, Disney talked about future expansion and reportedly said California Adventure has approval for 3 million square feet of theme-park space but has used only 900,000, according to Anaheim’s master-plan agreement with Disney. An on-line square foot converter tells me 3m sq = 68.8 acres and 900k sq = 20.6 acres. So that's 48.2 acres that can be developed.
Now I agree with you; I'm not seeing where all this space is either, but that's what was reported.