I read it, and all that quote illustrates is that the author doesn't know a great deal about NASA's development process. ScriptEase is not large, and purchasing it 17 years ago means that they had plenty of time to fully vet it individually, write their Host Objects and then another 15 years or so to test it.
For a low level view, as how the code actually should look like, I found the JPL C coding guidelines very useful. It had an effect on me on how I wrote C after reading it.
> 23. Place #else, #elif, and #endif in the same file as the matching #if or #ifdef.
Oh my. I bet that one has an interesting history! That thought has never even crossed my mind, and I did some fun stuff like include a header twice with different definitions to get a C++ mixin.
If you're curious about how NASA develops software - https://www.fastcompany.com/28121/they-write-right-stuff