Aren't cards based on time played?
I'm guessing SAM does this by a totally separate function than the "forge 'i got an achievement' message" thing. By automating the process of starting a bunch of games simulatneously or in sequence, and then closing them after a specified period of time. Just a guess, though.
Basically. SAM connects to Steam, and while it is connected, Steam thinks you are "playing" the game. This ups play time, and thus you can grind for cards without ever downloading or actually running the game.
