That interpretation of "clean room" is largely a myth in the context of open source reverse engineering projects. That level of rigour only really applies when you have companies directly opposed to each other, e.g. someone making unlicensed games for a game console by reverse engineering the DRM.

Clean-rooming is not a legal requirement to avoid copyright infingement; it's a legal defense against claims of copyright infringement.

In practice, the goal when doing open source projects like this, without a legal team to consult, is to use methods and approaches that yield a result similar to strict clean-room RE and result in an end product that is not a derivative work of the original code. The tricky thing here is that you need to be able to trust that the people doing the work knows how to do this safely.