rust?

It's not saying that "expert documenting for experts, the end" = "user documentation, though of lower quality"

It's saying that "expert that's bad at user documentation documenting for experts that can't figure it out from raw code" leads to "experts that are good at user documentation creating decent user documentation" with higher probability than the alternative.

Now, if you're saying that documenting how it works instead of intended behavior for end users doesn't necessarily help describe the intended behavior, that's a fair statement, but I'd argue that if you don't have both, you don't have adequate expert documentation either.