–Not legal advice-- Except he can’t do clean-room development because copyright is viral. If he had access to the copyrighted source, any code he writes on the matter, if it coincides with the copyrighted one to some extent, can be pursued for copyright claims (IBM v. Microsoft). For example, when there’s a leak of Windows source, ReactOS devs get super scared, because it really puts them on the line. Another example is Nouveau, which can’t accept anyone who has worked at NVIDIA. That being said, the company was not intending to do anything with it, so they can’t claim damages; ergo, he’s completely safe.