Wolf Blitzer got an exclusive interview with Balloon Boy and his family, and not surprisingly, BB himself (aka Falcon Heene) fails to shed much light on his motivations. Check out the video (with bonus fart) post-jump.
So he heard his parents frantically calling for him, and didn't come out of the garage — apparently because he hides whenever his parents are angry at him. What a wuss. Good thing he's only six years old or we'd sic our resident angry Spaniard on him for a bitchslap.
As an interesting little tidbit: It appears BB says "But we did this for the show" at around 0:45, which is immediately followed by a fart. No lie, go watch it. I'm not really sure what he meant by "the show": It certainly plays into suspicions that this was all done as an attention-getting stunt, but the kid was also on television once before and could have been referring to that. [YouTube]