Of course there is a relationship between aspergers and diet, but not specifically because a change in diet helps that condition.
A gluten free, and in many cases, dairy free diet is beneficial for everyone.
These diets alleviate digestive problems and promote weight loss in everyone, not just those with aspergers. Let's face it, the healthier you are, the happier you feel.
Few people realize that everyone is at least somewhat lactose intolerant, but some people can digest lactose better than others.