Your assumption is reasonable, but the author clarified on reddit that they had a much more expansive definition in mind. They want more than what is explicitly granted by the MIT License (the right to "deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software").
They want the right to fork, call their fork Rust and compete with the main repo for users. When asked how having multiple competing repos all claiming to be Rust would be beneficial to the Rust community they had nothing to say.
> When asked how having multiple competing repos all claiming to be Rust would be beneficial to the Rust community they had nothing to say
Being able to call the commands of a fork rustc, cargo etc would allow trivial drop-in replacement in case the official toolchain takes a bad turn (for example with analytics).
Furthermore, being able to use Rust in your fork's name (e.g. g-b-Rust) makes discovering better forks a lot easier, as opposed to the names insanity with Firefox derivatives
There's just little benefit for the public in this Mozilla's fixation with trademarks, open source thrived for decades without it
(I know that Rust is not in Mozilla anymore, but the legal culture evidently persisted)
They want the right to fork, call their fork Rust and compete with the main repo for users. When asked how having multiple competing repos all claiming to be Rust would be beneficial to the Rust community they had nothing to say.