Here's how it happened: Jason Campbell was hit by Aldon Smith in the end zone and fumbled. Bears offensive lineman Chilo Rachal picked the ball up and as he was falling, threw the ball forward and out of the end zone. The refs initially ruled that it was a forward pass, so they said it was incomplete.
And then they followed up with the ruling that if it was a forward pass then it was intentional grounding.
So that's how you get intentional grounding on an offensive lineman.
The 49ers, though, didn't agree with the call. They thought Rachal was done. The refs reviewed it -- technically their third ruling on this play alone -- and sided with the 49ers, ruling Rachal down and giving San Francisco the two points.