That's interesting to learn about the Linux APIs - not something I knew.
I'm still not sure about the GPL claims though. Imagine I write a Python script which is entirely my own - the only reference it has to a GPLd piece of software is an import statement and a few calls to some APIs.
The Google vs Oracle case made it clear that API usage (and even re-implementation) falls under fair use. The rest of that script is entirely written by me, and therefore I own its copyright. I could even develop the script entirely without running (or even having on my computer) any GPLd software at all - relying just on published documentation of APIs, the usage of which has been established to be fair use.
If I send you just the script. I'm not distributing a GPLd work. Maybe you could choose to run it on your computer, at which point it would resolve my "import x" statement as pointing to some GPLd software. It's only at that point that there's any linking. If you had a different PYTHONPATH setup, the same module might be a different, proprietary implementation, or a mock.
What basis does the copyright owner of the GPLd software have to come after me? I haven't accepted their license. The only person they could possibly have a case against is the end user of the script - who has violated the GPL by linking my non-free script with their GPL software. But if they're not themselves distributing the combined work, is there a case of copyright violation?