@dosnostalgic I think that just means top 2% by number of posts per year.
I'm in the top 3% somehow despite being very very very far from being popular here and I'm guessing it's a combination of (a) I quit twitter entirely and just hang out here a bunch and (b) the bottom 50% is probably all just accounts people created to check out the platform and then walked away from when they found a new shiny thing.