Dave had a good point - the view the ref had, Rose was completely blocking his view of Dyer's arm and the assistant that side was at the other end, which means that the referee was influenced by the crowd.
Definitely a penalty Should it have been awarded? Probably not. I can only assume the referee gave it on the definitive change of direction of the ball and the fact that there's no other way for it to change like that plus body language of the players. Unless the assistant told him handball penalty over the mic without flagging I can't quite get how the ref could actually see it from the position he was in. .
