Well, it might simply be "push the project architecture in right direction so whole team overall is efficient".

It's also probably a lot of anecdotes, "this dev solved weird issue in a day where other dev was stuck for week and couldn't find it!".

They might be 2x developer on normal day but happened to be this or that, debugged some hard bugs everyone else got stuck at and the people in project remembered those few good performances and assumed they do everything that much better