wolfsrain: It seems that is only for the people that already own the game as retail (also i've seen reports of this happening to peeps owning the Deluxe Edition).
darthspudius: Interesting, I have it on Steam and xbox haha.
From this statement, I have made the following conclusion and verdict.
At some point in time, you opened your obviously terrible Steam client in order to play a game of Battlefield Bad Company 2 online. At which point, you were requested to input your EA account credentials, and perhaps the CD key that came with the game, and you did both. Ideally, the EA account you used to log into the game is the same as your EA Origin account. Fast forward to today, you just discovered that Battlefield Bad Company 2 was added to Origin. This is natural considering you logged into the Steam version using your EA Origin account and then activated it on the EA Origin account.
This is not the only game that does this. On the first time launch (per each reinstall of the OS), Alice Madness Returns on Steam asks you to input your EA account details. If you input in an EA Origin account, and then open your Origin account, you'll notice you have Alice Madness Returns in your Origin account.
How do I know this much? I used to have both Steam and Origin open when I got Alice Madness Returns, and I noticed that. As for Battlefield BC2, well, I traded for a Steam gift of the game, then got the CD key from Steam and activated it on Origin and downloaded the game from Origin instead.
Feel free to criticize my reasoning, folks.