Is the boy really autistic?

Yes, the boy is autistic, and the mom's really a bitch. The Dad's a wuss. The show is actually a documentary about a family living in the West of England. It's all real. Really.

----------------------------------------------------------------------------------
You have meddled with the primal forces of nature, and YOU ... WILL ... ATONE!

I read in an interview they specifically chose not to have a child on the autism spectrum play Joe as to not force the child to go through the emotional aspect necessary for the show. The actor playing Joe is extremely talented and believable as a child on the spectrum. One of the common features of a child on the spectrum is not being able to express emotions in the "normal" way. Which has been highlighted on the show with the mothers expectations of Joe's response to Maya & that situation.