Hmm, I suspect for example "rambly long post" is more common ADHD trait on stimulants than off. Maybe that's what you're talking about?

Besides that, I think, generally, traits will be "a combination of reasons."

For example, even before stimulants folks w/ADHD had bursts of energy and attitude that can be similar to stimulant-driven quirks. Those quirks are probably just more common w/meds