Open source is not the same as source available. I’m not going to do a deep dive on definitions and licensing, but open source generally means that you are allowed to do what you want with it. It also usually implies that if the creator updates it, that updated code will also be shared.
The leaked Cyberpunk 2077 source code is from 2022 at the absolute latest (released 2024 from a hack done in 2022), is not open source licensed for re-use (meaning any use of it by people outside of CDPR is illegal), and they have released numerous patches, updates, and an entire DLC since.