> Prior to the study, 83% of participants had "severe" autism. Two years later, only 17% were rated as severe, 39% as mild or moderate, and incredibly, 44% were below the cut-off for mild ASD.
Emphasis mine. If you are below the cutoff for mild ASD you wouldn't be diagnosed at all.
(Without a control group, you have questions about how people of that age generally progress, and what other treatment/therapies they receive over those 2 years. The phase 1 trial was with children whose parents presumably sought ever possible way to help them, while the placebo controlled phase 2 was adults who may have plateaued.)
Which leads me to wonder if for some of these children is the root cause just gut issues.
If all they have figured out how to so is treat significant gut issues that sounds very promising.
That makes sense, since ASD is a disorder classification and is mainly relevant for treatment and benefits. Plenty of autistic people are not diagnosed with ASD.
The article certainly could do more to differentiate between the autistic spectrum itself and the diagnosis of ASD, but as long as you know not to conflate the two, it seems perfectly clear to me.