Trying to be charitable I think what they mean to say is “people with medically untreated ADHD who have been managing their symptoms with structure and routine finding their strategies failing in a new environment they have less control over.”
Given the context, it also might be a sarcastic illustration of people's misunderstanding of ADHD as a sporadic condition instead of a neurological disorder.
The article makes no attempt to define ADHD or even say it's a valid diagnosis in adults. In fact, it implies otherwise.