The very fact the school thought it a good idea to give a student a disciplinary role is ludicrous. Unless the person is a sixth form student, I can't see how another student is ever going to pay attention to their orders. Particularly as, in my experience, the prefects are generally the less popular kids anyway. It is only ever going to generate bitterness, promote confrontation and conflict and put students in impossible situations that they shouldn't have to be dealing with. For christ's sake, there are teachers who can't control the pupils, let alone getting other pupils to try to control them.
It was irresponsible of the school to give the kid a disciplinary role, regardless of whether or not he is autistic. And, if he is autistic, it is especially cruel to him to put him in a position where he will regularly face confrontation. Even if he volunteered for the role, it is the duty of the school to act to look after their pupils, and they failed him. The school needs to seriously re-address its use of prefects.