Graydon tweeted https://twitter.com/graydon_pub/status/761280391239958528 and it's all clear now: the Mozilla Summit session was called "Project Servo" but focused more on Rust, and Graydon's slides had that phrase as title:

http://venge.net/graydon/talks/intro-talk-2.pdf

(also picked up on my T2 robot from the future joke and reversed it, lol). But Rust was Rust, even then. Servo was the big news, I think Rust was known within Mozilla, a bit. So we used Servo in the session name and the rest is history.