That's a misrepresentation.
Unmedicated ADHD people have a stimulation deficit and the reason why they're hyperactive, either mentally or physically, is because their brains are struggling to become stimulated enough.
Regarding coffee: this is the unmedicated ADHDer's friend. It can calm people down. But others, like me, who have a formal diagnosis, are heavily affected by caffeine and it will keep me up.
Meanwhile, my partner does not have ADHD and she can drink coffee and sleep fine.