From the source paper they link to: "Given our longitudinal design, we did not split our participants into cases versus controls. Through the years, symptom scores and diagnoses varied through time and participant characteristics changed from wave to wave (Fig. 2). Some individuals originally recruited as controls or unaffected siblings developed ADHD at a later time-point and others recruited as ADHD participants remitted, further highlighting the complex, variable course of ADHD. Alternative to a case-control categorization, ADHD can be operationalized as a continuous trait (Lahey and Willcutt, 2010, Marcus and Barry, 2011). In a previous cross-sectional study, we systematically showed that, compared to categorical diagnoses, continuous symptom measures are more sensitive to diffusion-weighted brain features in this sample (Damatac et al., 2020). Thus, all models here used symptom scores, optimally capturing the dynamic and continuous nature of the ADHD spectrum throughout development in this longitudinal cohort."

Also, only 2-3% coexisting anxiety seems like it is not representative of the average populace with ADHD. It further does not seem to address dopamine dysfunction.