How pure does your program have to be to be rust for you? How few libraries in C or C++ must it call? The developers are writing all their code in rust, so it is in rust…
It’s a UI library that’s showing UI controls that are written in C. It’s dishonest to call it Rust because it wraps those controls in a layer of Rust
By that standard no binary that links against glibc, whether originally written in rust or go, is in fact rust or go.