Ya know, it was pretty clearly laid out it seemed back in the 00's when I even first had copyleft explained to me.
There is copyright. Everything has it. There is also copyleft. It's an act of copyright. Comply by sharing when asked, or you've violated the terms unless you negotiated some alternative arrangement ahead of time.
I look at all the hand wringing by the legal profession and I just have to shake my head in confusion in how the semantics on this are still contested so in a profession where we even acknowledge that what is written may not be reflective of the original intent.
Then again, billions of dollars worth of captive audience/free developer hours are up for grabs. Suppose I shouldn't be surprised.