I have heard the same.
I have ADHD and caffeine has a calming effect on me after a very brief stimulant effect. I don't drink much caffeine anymore because unless I'm extremely regimented about the exact same amount every day, I get withdrawal headaches or migraines pretty easily. When I used to drink a lot of coffee I could brew a pot of French press, drink the whole thing in short order and have no problem falling asleep right after.