The GitHub Blog featured the top ten from this years competition. The picture comes from The Last Spartan which I really liked. Ironically the screen grab image was 121KB, almost eight x the size of the actual game!
However the internet taketh and the internet giveth. If you paste this (or any of the source listings) into an online deminifier (aka beautifier) such as beautifier.io then you get all 1622 lines laid out in immaculately indented glory. It’s actually 73KB in size as a normal listing and still very impressive.
There’s no reason why games can’t be done this way i.e. drawing graphics in C+SDL2 though I doubt I’d get them down to 13KB. My asteroids game which was 2200 lines of C generates a 96 KB exe. But when you add in images, SDL code and sounds etc it comes out at just under 35 MB.