User blog comment:Zelron/The Elder Scrolls V: Dragonborn rumors (Imbedded deep the secrets sleep)/@comment-69.235.12.208-20121022034255/@comment-3492791-20121022043843

That is a practice called Code locking. All the actual data for the DLC is given to people beforehand, and the "DLC" is actually just a code that allows access to the content.

You can imagine it as things like on-disc DLCs.