EA has included a new mode in NHL 2011 that's based on an electronic CCG. You collect players, skill enhancements, jerseys, and other equipment and build a team to manage and play online against other players. At the heart of all this is still the best hockey video game on the planet, but it adds something different to the franchise and season modes.
So now, to promote the game and get the word out about the new game mode, they're offering what amount to free "booster packs" for playing the demo and then sharing a link about the game on facebook. Like with any other CCG your chances of success are boosted by having the best cards. No info is available about what cards will be rare, but more booster packs can't hurt.
I don't know exactly how they can track all this, but I'm guessing there's something to the link they have you post.