The Windows as a porting layer story is a whole subject in its own right. But the WINAPI macro was a porting thing.

But this is an example on this very page of the telephone-game problem that happened during the Operating System Wars, where the porting tool of the WINAPI macro that Microsoft introduced into its DOS-Windows SDK, allowing 32-bit programmers to divorce themselves from the notion of "far" function calls that 16-bit programmers had to be very aware of, becomes intertwined into a larger "Windows is a porting layer" tale, despite the two being completely distinct.

That a couple of applications essentially supplied 16-bit Windows as a runtime really was not related to the 16-bit to 32-bit migration, which came out some while after DOS-Windows was a standalone thing that one ran explicitly, rather than as some fancy runtime underpinnings for a Microsoft application.

* https://jdebp.uk/FGA/function-calling-conventions.html#WINAP...