Are you familiar with the GAPS Diet? The author claims to have healed her son's Autism through dietary changes. She does consider Autism as related to inflammation, particularly through the gut flora.

Paleo will help your child, although definitely don't cut down dairy, use goat/sheep mostly instead, and only butter/cream from cows. However, for even higher results, you might want to look at the Paleo-ketogenic diet, that restricts carbs to less than 40-50 gr per day. The body switches to fat for fuel in that case, and the brain runs on ketones instead of glucose. Bipolar (and many other mental disorders) benefit from the switch to ketones, since the brain chemistry changes. Make sure you include many fermented foods and other super-foods, I have a list here, which helped me immensely getting my health back on track: http://eugenia.queru.com/2012/03/05/top-10-must-eat-paleo-foods/

I'm so glad that there are so many people who have such a clear understanding of what austism is and how to treat it! The fact is that no one knows what causes it or how the symptoms are related. Do what Doctors do. Try different things one at a time and see what works for your child. There is not enough data to make generalized or definitive statements. Science will eventually enable genotyping of the different patient types that obviously exist and enable to us to hone in on what works for who.

What kind of diet is he currently eating?

It appears that article is one of many instances where anecdotal evidence is admonished as real science in the case of Autism causality. Current scientific research suggests that the relationship between Autism and gastrointestinal distress/sensitivity appears to be related to the genes implicated in the Autism Spectrum Disorder. Meaning, currently 15 different genes are implicated in Autism, and some of these genes also put individuals at risk for gluten intolerance, lactose intolerance, etc. The best understanding of Autism at this time is that intestinal inflammation does not cause Autism; it's genetic. If you are interested in reading more about the history of Autism research and how a few horribly unethical researchers have changed the public's understanding of why Autism occurs, read "Autism's False Prophets: Bad Science, Risky Medicine, and the search for a cure" by Paul Offit.

Autism is very different from ADHD and Bipolar Disorder. Neither of these disorders are caused by intestinal inflammation. They too are neurochemical and influenced by genes. I say definitely go for a healthy diet, but don't expect the symptoms to dissipate because your child has stopped drinking cow's milk. Good luck with your efforts to keep your family healthy.