So the source was mostly recoverable from the game that shipped. This was only discovered in 2016.
There was a similar thing I sometimes encountered in MS-DOS games. I would see snippets of the game's source code when I was idly perusing the executable. (You did that too, right? And you also loaded every kind of file up as a sample in Scream Tracker, just to see what it sounded like, didn't everybody do that?)
My hypothesis is that C compilers of the era would allocate space for fixed-size arrays when building the executable image that got written to disk. If the array was initialized, the data would go there. If the array was uninitialized, whatever used to be in that memory would still be there.