This does not imply causation. Someone with ADHD is more likely to give in to distraction and dopamine. This study was done with a sample of people who already have ADHD. Nothing in it indicates that television time is going to cause ADHD.
Someone who has a better relationship with exercise, screens, or whatever, doesn't mean they don't have ADHD anymore. Medicated or not. They just have better support and lifestyle habits that minimize how much it might impact them.