It might be a disorder, but that doesn't mean they don't have one. After all, it takes a lot more work to develop a theory of mind about someone who's not like you (as people with autism have to do every day) than to assume everyone you meet is like you (like most people can get away with most days).
The theory is controversial, and there are many details that are argued about. I certainly don't have a view as to which is correct, but I do think the debate is complicated by the definition of "autism." I do agree with people who believe it is a cluster of underlying conditions with some overlapping symptoms that are bundled under the same umbrella.
