Yep , as i recall this was the original 'clean room' implementattion that was made with regard to IBM clones and the BIOS program that was used to initialize them.

Also a few years bcak theer was the csae of SAP(?) i tthink where they did a reimplementation indipendently via the design documents.

Those two were upheld on litigation and bear out to this day.

This case however is neither a clean room implementation nor relicensable.

A good example if the author had wanted to be correct would have been the sudo rewrite , which ubuntu is doing with their sudo-rs in rust.Not bug for bug compatible as they have already deviated from some usablility choices but more valid than this.