This being written in Rust tells me it's probably going to be fast/lightweight. Go would be a similar expectation. If it's written in Rails I'd have different expectations. Python or Node might fall somewhere in the middle.
This project is a webserver you can host yourself, so having an idea of the resources required is very helpful.
Which is exactly why the language doesn't matter. It being written in rust doesn't tell you anything, and serves only to evoke some predisposition you have for rust. There's nothing in rust that stops users from writing horrible algorithms. This reddit front end could send separate requests for every letter it loads for all you know.
It's similar to Big-O notation, seeing that it's in Rust gives me an idea of performance profile to expect. If it's a Rails project I know that the best case scenario is fairly resource intensive, no matter how good the code is. If it's Rust then I know that for an average quality open source project it will be lower resource usage. If a project ends up being terribly inefficient after that, I'll drop it regardless of what stack it's in.
Knowing what tech stack something uses is a valuable first signal.