The Wine developers are allowed to read whatever they want. They may choose to have a policy not to, because it makes it easier for them to prove that they didn

The Wine developers are allowed to read whatever they want. They may choose to have a policy not to, because it makes it easier for them to prove that they didn't make unlawful use of proprietary code: they can't have copied something that they never read. If you reproduce something independent of knowledge of the original then that is a defense against copyright infringement. This is essentially the "Clean Room" tactic: https://en.wikipedia.org/wiki/Clean_room_design https://en.wikipedia.org/wiki/Clean_room_design