Did they “gave away”? Or did they merely contribute it? Two different things.

I don't see the difference, I said gave away but for me it meant the same as contributing their own code for someone else to use.

“Silence obligues”, in which case it means “the fallback applies which is a) I retain the copyright if there was no CLA signed that waived my rights or b) you retain the rights if there was such a waiver of rights”. Ez pz.

Alternatively, Implied license. From the article:

This doctrine posits that a copyright holder may grant permission to use their work without an explicit agreement, based on the circumstances surrounding the creation or distribution of the work. Implied licenses arise when the actions of the copyright holder reasonably suggest consent to use the material, thereby creating a legal understanding between parties.

If their code was for example made specifically for that project or they approached the project to contribute their code, that forms an implied license through the actions of the copyright holder.

He wouldn’t need to, is the point.

Under implicit license he needs to. Or rather he needs to prove the implied license does not apply.