I think it might be one amongst many indirect signals for code quality.
It's a hard language, so the author of the program likely has at least some amount of prior experience to build off of, and to build anything truly substantial with it you have to have a deeper understanding of how the code actually works than you do with some other languages.
The language does do error handling, type validation, memory safety, and null checks really well. So, it's safe to assume that the app may have fewer bugs than it's counterpart written in, e.g., C or JS.
It could still be shit, of course, but I imagine the average quality of an app written in rust would be at least a little higher than thay of apps written in many other languages.
Bug free is a part of usability. Can't use an app if it's broken. I doubt the language used has any significant impact on the inherent usefulness of the application's created with it, but I don't think anyone is making that claim to begin with.
I mean, was the Linux desktop any good, 20 years ago...? It didn't really matter, what mattered is how cool the idea of it was (or was perceived to be).
