Many critics of institutional psychiatry hold that the construct of mental illness is often used to medicalize nonpathological behavior that doesn't meet social norms, putting a scientific stamp of approval on judgements regarding human behavior, morals, and ethics.
Given the uncertain pathophysiology of ADHD, the degree to which symptoms resemble moral judgements, the dramatic increase in diagnosis following advocacy in the psychiatric community, and questionable improvement of long-term outcomes for patients treated with medication, ADHD is seen by them as a good example of this point of view. I assume that's what he was alluding to.