It was a joke. Did they also say double power-up points? If so, it's a joke.
If it's a joke, then I don't get it. What's funny about it? Where's the punchline? It also says for Assassin's Creed Revelations you get an extended gameplay mission, a weapons capacity upgrade, and a multiplayer skin... Haha? Yeah... that's hilarious.
Also, what it says is "double power up rewards points", which I believe refers to some sort of redeemable points system that gamestop has. They've given them to me when I've gotten other games from them in the past.