Interesting - that is not what he has been told however - He was told if players form both teams encroach not to order a re-take. I'll get him to ask at his next refs meeting
My son is a qualified ref and I asked him about this.
Apparently they are told that if players from BOTH teams encroach then not to give anything.
He said that if the Stoke player had not encroached as well the penalty would have been retaken but because both Dunk and a Stoke player encroached...