Determination of Winners. Sponsor shall choose the winners from all entrants who have submitted an entry prior to the Deadline. 3 Grand Prize Winners shall be chosen by Sponsor at its sole discretion based upon which entrants submit a Map that is the most fun, compelling, innovative and/or different. The decision of Sponsor is final. Prizewinners will be notified by e-mail within fourteen (14) days thereafter. To claim a prize, winners should follow the instructions contained in their notification.
And I am fairly certain that the winners have to keep that confidential until the winners have been announced at BlizzCon.
The way Blizz handled stuff with winners the last years (from the WoW area) was that they invited them via e-mail and they had to keep their mouths shut. During BlizzCon, they announce the winners to the public on a panel with a few videos. So, well, we gotta wait 2 weeks :)
Oh, I have no doubt that the winners have already been chosen and notified. Thats obvious. Im just rather skeptical of anyone that says "Hey I won, I got so much $$$ and going to blizzcon!". I see that behavior all too often.
But if he did win, then gratz to him indeed. But I`ll pretty much be set on believing it when Blizzard officially reveals the winners.