I would be surprised if he said that, because that’s blatantly incorrect:

www.frontiersin.org/articles/10.3389/…/full (Table 2, for example).

Schizophrenia, bipolar disorder, and major depressive disorder all produce or are associated with executive function impairments that are more severe than ADHD. ADHD is the only one of those with its specific pattern of attentional and reward-related abnormalities, but broad EF deficits are common across forms of psychopathology.