In the linked Rust graph, eddyb (the third-highest committer) is a volunteer (an unimaginably prolific one), not a Mozilla employee. kmcallister (the fifth-highest committer) is a Mozilla employee, but not actually on the Rust team (they work primarily on Servo (though there is a fair bit of spillover between the two projects)). Rust has a few other full-time Mozilla employees that aren't represented on that chart for whatever reason (working on feature branches, perhaps?), such as nrc and pcwalton.