I think I would say they must be mentally "off". Not a diagnosis category but clearly those people are somehow different if they can so easily do things that make everybody else appalled, shocked, sad and disgusted, not necessarily in that order.
BBM. I'm not sure what that's supposed to prove - it's to be expected if he had Asperger. People with Asperger syndrome are by definition relatively high functioning cognitively. It's one of the diagnosis criteria actually: if there is a significant delay in mental development then you don't diagnose the person with Asperger's syndrome. So if you have someone with Asperger syndrome you wouldn't expect them to be completely helpless in every way and if they aren't it surely doesn't mean that the person just uses the symptoms to manipulate others.
DSM-IV:
http://www.autreat.com/dsm4-aspergers.html
That is not to say that there might not be a manipulative aspect in there somewhere but just the fact that he wasn't obviously retarded in every area of his cognitive functioning doesn't prove he faked his difficulties just to annoy mom.
Anyway, "nothing wrong" in his cognitive thinking may be a little too strongly worded. We don't know that. People with Asperger's may have uneven cognitive functioning, high in some respects and more difficulties in other areas.