> How would you explain to a non-technical person that a kernel module is not a derived work?
GPLv2 does not use the term "derived work" anywhere. It uses "work [...] derived from the Program", and does not define this term [1].
I'd start out by explaining that before we even get to the question of whether or not the module is a "work [...] derived from the Program", we have to ask the question of whether or not the license even applies. GPLv2 only applies if the module does something that requires permission under copyright law. The copyright law question that needs to be asked is whether or not the module is a "derivative work" of the kernel.
> Can you remove the Linux kernel and still have a complete and working program? What happen if one removed all function calls to the Linux kernel or use of internal kernel variables? As a module, does it work with any other kernels like windows or apple, and what was the programmers intention when writing it?
None of these questions are actually relevant to the copyright law question of whether or not it is a derivative work. They are relevant to the question of whether or not it is useful when not used in conjunction with a Linux kernel but that's not a copyright law question.
To answer the copyright law question of whether or not some program P [2] is a derivative work of some other program Q, you only need to look at the source code to P and Q. If P and Q interact with each other (unilaterally or bilaterally, directly or indirectly) some people get hung up on the mechanism of that interaction, but that's not relevant to the question of whether or not P is a derivative work.
Whether or not a program P that uses function names, function argument ordering, and data structures of program Q, but does not copy algorithmic code from Q, is a derivative work of Q is going to essentially come down to whether or not the interface (I'm including data structures as part of the interface) of Q is copyrightable.
If program interfaces are copyrightable, then programs that interact with other programs will be derivative works of those programs, regardless of whether they interface by static linking, dynamic linking, system calls from a user process P to kernel code Q, IPC from process P to process Q, RPC from process P across a network to process Q on another machine and so on.
If program interfaces are not copyrightable, then as long as all P incorporates from Q are interfaces P won't be a derivative work.
Generally, courts have held that program interfaces are not copyrightable (with the notable exception of the Court of Appeals for the Federal Circuit in the Oracle vs. Google case, which does not set copyright precedent).
Thus we arrive at the major question for kernel modules: what copyrightable kernel elements do they incorporate?
If they just incorporate non-copyrightable interfaces then a kernel module would not be a derivative work of the kernel.
That's not the end of the inquiry though. It would be if some third party were making and distributing the module. E.g., if I were to write a kernel module that does not incorporate any copyrightable kernel elements and distribute it stand alone, for others to download if they want and use it with their kernels, we'd be done.
In the case of a distribution vendor distributing a kernel module along with a kernel, then even though the module itself might not be a derivative work their distribution as a whole is. Questions might arise as to just what constitutes a "work". If they statically link the module to the kernel, the resulting binary is clearly a work, and it is a derivative work of both the kernel and the module, and so the module would have to be GPL. It is important to note in this case that this is because the combined work is a derivative work of the kernel...the module itself is still not a derivative work of the kernel.
How about if the module is dynamically linked, but the configuration they ship automatically loads it at boot time? Might one argue that the kernel, init scripts, and dynamic modules together are all one work that the vendor is distributing?
[1] For completeness, GPLv3 does not use "derive" or "derived" or any similar terms it all. It uses the term "covered work", which is defined as the original program or a "work based on the Program", and it defines that as basically a work that requires copyright permission.
[2] I'm going to use the term "program" expansively to include modules, applications, plug-ins, and so on.