AFAIK the only thing that's straight up illegal to look at in the USA is child porn.

You can read bomb-making instructions, for heaven's sake. You can certainly look at this code. Just don't base a product on the ideas you got from looking at it.

The problem is how do you prove you didn't base your ideas on what you saw? If you never saw it then its easy to say you can't have copied it.

Copyright is about copying.

Are there any verbatim copies of the original in your project. Did you sign an enforceable ip ownership or non-compete agreement with GitHub about trade secrets learned while working on their source code?

If the answers to those questions are no, there is a very long, very steep, uphill battle facing GitHub.

Legality aside, the clean-room FOSS projects won't like your contributions if you have been exposed to the respective leaked source codes. From the top of my head, WINE requires this: https://wiki.winehq.org/Clean_Room_Guidelines