FBref.
I believe it's comparing him to other central midfielders in his league, but I could be wrong.
Edit: He's compared to players in his position from "Men's Next 8 Competitions (American Major League Soccer, Brazilian Série A, Dutch Eredivisie, English Championship, Mexican Liga MX, Portuguese Primeira Liga, Copa Libertadores, UEFA Europa Conference League)".
https://fbref.com/en/about/scouting-reports-explained
One way it might be skewed is he's compared to sitting midfielders, which he is but he seems to get forward a lot, too.
FBref separate defensive midfielders from attacking midfielders/wingers.