I guess they just flipped a coin and according to it they chose the pic, that's the only explanation unless they thought that an angry pic would help sell Xmas album.
EDIT: Just watched the SUBG performance. It was awful. Idol contestants need to learn that it's a law of physics to never sing a Kelly Clarkson song. It just doesn't work.
I was curious and watched it just now and I can't stop laughing on the train. I have nothing but Demi shade and criticisms.