Had no idea there were so many experienced medics on this board, but their contribution is well made!
I may not be a medic, but clearly events would prove they've got it wrong in this case. In fact I'd go as far as to say imo the club's medical staff has let down Mike rather badly here. Whoever passed him as fit to play should be getting a rollicking.
Harsh judgement; if it was an anterior dislocation then research dictates that the reduction should have been Followed by surgical, due to the high probability of repeat dislocations as a direct result of rotator cuff, ligament and capsular damage. However, if the dislocation was posterior (head of humerus pops out towards the back) then if the area retained good mobility, and the rotator cuff remained intact then it is possible, and fair to believe that Closed Conservative reduction with physio may be the best route, especially considering the unusual position the joint would have to get into to re-dislocate i.e. the classic behind the back arm lock position that you learn in the playground; but to complete dislocation!
Of course, it could be that whilst the club is saying that it is a dislocation, it could be something entirely different, such as a SLAP lesion, or (labrum tear) this is the piece of cartliganous tissue that makes the shoulder socket deeper and ensures that the head of the humerus is congruant to the socket. The club may have just released the dislocation as an umbrella term which, the pay person can associate with.
Either way it is reasonable that both the club and heywood (let's not forget that as a consenting adult he would have give informed consent to any treatment; I.e. he would have to be told and understand the implications of surgery/non-surgery) would come to the conclusion that non surgical intervention may be the best course of action in the immediacy of the injury.