That is an obviously false dichotomy. The author of the comment never mentioned Rust, and wasn’t asking about Rust. Such a false dichotomy feels like flamebait, which is against HN guidelines.
Your false dichotomy also implies that “unsafe” blocks are as unsafe as C++, which is not true. “Unsafe” in Rust turns off very few checks[0], most of them are still active. No one would write a serious Rust program entirely in unsafe anyways.
Regardless, asking about security considerations is a valid thing to do, even if it were written in Rust. Security is not just about memory safety.
Furthermore, choice of language can have an effect as to the actual security of the networking layer.
Having parsers (and serializers) proved absent of runtime errors (e.g. with something like SPARK) is a form of guarantee I wish I'd see as the default in any 'serious' network-facing library or component. It's not even that hard to achieve, compared to the learning curve of the borrow checker.
Once rust gets plugged into Why3 and gets some industrial-grade proof capacity, the question of 'is it written in rust?' will be automatic (as in 'why would you do it any other way?').
Your false dichotomy also implies that “unsafe” blocks are as unsafe as C++, which is not true. “Unsafe” in Rust turns off very few checks[0], most of them are still active. No one would write a serious Rust program entirely in unsafe anyways.
Regardless, asking about security considerations is a valid thing to do, even if it were written in Rust. Security is not just about memory safety.
[0]: https://doc.rust-lang.org/std/keyword.unsafe.html#unsafe-abi...