After browsing that page, I observe that even when Cython is wrapping an external C library, there's still a notable difference between the way Cython does things & the way Pymod does things.
The explanation on that Cython page begins: "To get started, the first step is to redefine the C API in a .pxd file, say, cqueue.pxd". So to wrap an external C library using Cython, you still need to define an entirely new header-like definition file in Cython's intermediate language.
In contrast, Pymod only requires an `exportpy` pragma annotation at the end of an existing Nim procedure function header -- you don't need to create any intermediate definition files. And the `exportpy` pragma is inert unless you invoke the "pmgen.py" script (a Python script in Pymod that determines the Python C-API system configuration & automates all the compilation), so your Nim code is still completely valid Nim code after you apply the `exportpy` annotation.