To clarify: the “Rust team” that Emily has joined is the team of Mozilla employees working on Rust. But Rust itself is a community project that stretches far wider than Mozilla.
The teams on the page you linked are the primary decision-makers for each area, drawn from the whole Rust community. Being a Mozilla employee working on Rust doesn’t (and shouldn’t!) immediately mean you are an expert qualified to be a member of these teams – you have to work your way there, just like anyone in the community. But we fully expect Emily to join the Tools/Infrastructure team, and perhaps others, over time – as @Manishearth says, probably in fairly short order.
