The argument is not esoteric. An Apple employee working on a reverse engineered GPU driver might (intentionally or not) incorporate internal knowledge that they are contractually obligated to keep secret or write an implementation that is too close to proprietary code they had access to, to the point that it could be argued that it is a derived work.

This sort of thing has always been a concern for projects that re-implement some existing piece of software, e.g. there were concerns early on during development of the GNU project about people contributing after having been exposed to Unix source code. Similarly, it is an ongoing concern for the Wine project[1], as well as ReactOS. The later even had a code freeze and internal audit in 2006, after allegations came forward that code had been derived from disassembled Windows binaries[2].

[1] https://gitlab.winehq.org/wine/wine/-/wikis/Clean-Room-Guide...

[2] https://en.wikipedia.org/wiki/ReactOS#Internal_audit

Wasn’t that exactly the legal standard Compaq had to prove when they did a clean room implementation of the IBM BIOS?