Another implementation is still unlikely to have the exact same bugs. Especially rewrite in Rust will force the code to be structured differently (Rust is very opinionated about that).
The spec is big enough that the team won't be able to just write the exact same implementation from memory.
I don't disagree that it's sufficient, but also, ideally different people would implement the spec. If you have a particular mental model or understanding of a part of the spec that doesn't match what the spec actually says, that is likely to translate identically when writing a second implementation.
Another implementation is still unlikely to have the exact same bugs. Especially rewrite in Rust will force the code to be structured differently (Rust is very opinionated about that).
The spec is big enough that the team won't be able to just write the exact same implementation from memory.