Great job on caring for him. The reason most vets recommend euthanizing chickens is b/c they do not view them as pets. Many dogs live with one or two legs missing and have yet to find someone who thinks this is cruel. It is all a matter of perspective,you view your chickens as pets(i view mine as pets also and would have done the exact same thing)so for you this is the right decision.
Best advice,pay no attention to what others say,only matters if the decision you made feels right to you and in your case i believe you have made the right decision for your boy,he looks very content and happy.