Having read the article fully, I feel that your line of argument here is kinda unfair.
When they referred to different symptom sets, their emphasis were on things like anger, risk taking, mood lability. Sure the particular line about hyperactivity probably doesn't support the point as the others, but it isn't key. When criteria become this broad, you really have to ask questions. The fact that adult ADHD is associated with so many comorbid psych 'disorders' (like everything in psychiatry) and inattention is prevalent in basically everything is more to the point.
The arguments about ADHD being a neurodevelopmental disorder are also valid. If it is, why would something like 'adult-onset' ADHD exist in the first place? It sounds like something entirely different, especially if the sex differences flip.
Key to understand their line of thinking is that the arguments above do not prove that adult-ADHD doesn't exist. Their key assumption is that the null hypothesis is that it doesn't exist, and so if you want to create a separate diagnostic category, you have to disprove the null hypothesis and show the evidence for diagnostic validity, and you have to answer these questions with evidence. That's the whole point of scientific rigor and the inherent causality underlying the medical diagnostic system. Of course I'm not sure there's a DSM diagnosis that meets these criteria anyway, so lol, we kinda know the answer there.
And I'm sure there will be someone that says, 'oh but stimulants work! so ADHD makes sense'. I don't think we needed a separate diagnostic category to know that stimulants can improve attention deficits on the short term. This is another key to their line of thinking: there's a whole lot more of implied assumptions when a new diagnostic category is created.