Well, whether the hacker stole the beta and source code - it wasn't his fault that the game is delayed. The game simply was not finished - unless the hacker stole everything and destroyed all copies on servers, deve boxes, in the CVS repository (or where ever they keep their file versions), etc.
The developers simply weren't finished, and perhaps even "staged" this hacker to use it as an excuse. I don't know that for a fact, but who cares? The game wasn't done.