Rust usage is growing pretty quickly, a lot like C++ at its age. "Extremely" is a meaningless term in this context.
"Used by <Big Company>" means much, much less than most people who mention it believe. The bigger the company, the more likely it is that they use literally anything at all you can think of, and the correspondingly less it means that they do. They might even be using it in a certain project deemed strategic. But we all know how many of even "strategic" projects at big companies end up canceled, even when they seemed to be a success. You can be certain that they are not using it for anything central to how the company makes its money.
It is more interesting when a $company uses $newtech where it will only have an income if the project succeeds. But you probably never heard of $company, otherwise, so have no way to evaluate how important it is.
SpaceX has said publicly it uses C++ for mission-critical work. Like other $billions companies, they do a lot of things. Saying they do Rust, too, makes them seem edgy in circles where people are likely to hear about it, regardless of how much they actually depend on it. So it is really hard to tell.