Yeah, doesn't make Rust's dependency on C++ go away for its safety.
The point is the "look at what I say, not what I do", when talking about safe languages and dependencies into C and C++ libraries and compiler toolchains.
It has to do with yours incorrect assertion that using C++ in the runtime is a disadvantage for C# in regards to Rust, which equally depends on C++, in both of its compilers toolchains, rustc and gcc-rs.
When Rust gets fully bootstrapped in self hosted toolchain you'll have a point.