I think there's lots of value in wrapping a raw/unsafe implementation with a rust API, but that's not quite what most people think of when writing code "in rust".
The code has a C style to it, but that doesn't mean it wasn't actually written in Rust -- Rust deliberately has features to support writing this kind of code, in concert with safer, stricter code.
Imagine if we applied this standard to C code. "Zlib-NG is basically written in assembler, not C..." https://github.com/zlib-ng/zlib-ng/blob/50e9ca06e29867a9014e...
We absolutely should, if someone claimed/implied-via-headline that naive C was natively as fast as hand-tuned assembly! This kind of context matters.
FWIW: I'm not talking about the assembly in zlib-rs, I was specifically limiting my analysis to the rust layers doing memory organization, etc... Discussing Rust is just exhausting. It's one digression after another, like the community can't just take a reasonable point ("zlib-rs isn't a good example of idiomatic rust performance") on its face.