Well as the article says:

"Metabolism is the language that the brain, gut and immune system use to communicate, and autism occurs when the communication between these systems is changed"

So it's not unreasonable that for some people, dietary interventions can have some effect on this interplay between systems. Mostly a just a random "YMMV" shot in the dark at this point. But hopefully as this research advances, more targeted and predictable treatments will emerge.