It was certainly a red card as contact with the head from the shoulder but I don't think it was as bad as people are making out.
Walmsley is crouching into the tackle, he is not late enough to be negligible and it wasn't a shoulder charge as it was an attempted tackle.
The issue with them tackles on HBs is when players are not making a genuine attempt to tackle and fly in with just their shoulder: e.g Joel Tomkins on thurs was very late and used a shoulder charge and scott Taylor on GOB last season.