This chart was made by ousted homophobe Br*ndan E*ch who clearly has a particular axe to grind, and the right side of its Y axis is a normalized value for some reason, but its point stands.
I wouldn't call it them "doing" Rust in that they don't have any exclusive control of it, just being (major, I think) contributors. But I'm not really familiar with this so perhaps my perspective is wrong.
Unlike Firefox, Rust would continue on quite well without Mozilla but I doubt that Servo and the other web rendering projects under that umbrella would survive. I'd expect most people working directly on Rust itself at Mozilla would be able to continue doing that elsewhere.