My impression, Almunia is going for the ball which bounced away from his hands. He did not deliberately bring down Rooney. Notice Rooney's trailing left leg, it is dragging deep on the pitch which suggests that he was already going down much before contact having already lost control of the ball. So it is he who should have been booked. Mike Dean got this wrong too.
Again, this shows why video technology is so important.
Hat tip to Harsh who sent this.