Perhaps a silly question, but is this entirely legal in the US? This is, can I just download the source code and look through it without any major caveats like

Perhaps a silly question, but is this entirely legal in the US? This is, can I just download the source code and look through it without any major caveats like already owning the corresponding game or having permission from the publisher? I see that some of the source code has a license associated with it, e.g. licenses claiming that the content's in the public domain, but I'm unsure if such licenses are necessarily legitimate.