Mitchell's arm was getting pinned well before the image you posted.You are not allowed to reach all the way around the player like Mitchell did. This angle in the video doesn't show it well but the picture shows he was reaching all the way around simmons before he pinned his arm to him. The ref could spot this pretty easily from his angle.
I know everyone wants to be upset about all the bad calls. There were bad calls, this wasn't one. We also played like **** at the end. This one is on the Jazz for the loss.

Just stop.