That is great that you found something that works for your child. Unfortunately, it may have nothing to do with autism. Autism is diagnosed based on a collection of behavior. The problem is, much of that behavior also occurs in other disorders. It may be the case that something is called autism when it is, in fact, it is an entirely different disorder. In your case, it could be a dietary/digestive/etc.disorder (again, that looks like autism because no behavior is unique to autism).
At the end of the day, autism is not a disorder of diet or digestion and, therefore, is not resolved by changing a diet. Regardless, if you’ve found something that works for you, that’s great and, in the end, the label is rather unimportant.
Diet plays a critical role in the management of ADHD. Take a look at Dr. Daniel Amen’s work on the issue.