So it turns out this is not "unlike Rust", it's pretty much the same thing: if everything was built in safe rust, then it would be as safe. The communication of this point is not great at all, so much so I don't think it's purely informative.
Safe Rust still basically always links against unsafe C libraries though. Fil-C will only link against libraries compiled with Fil-C which makes for a vastly stronger guarantee.
Also, plenty of code written in Rust is not safe so "if everything was built in safe rust, then it would be as safe" does not hold. There's definitely no way to write safe inline assembly in Rust.