Late reply but!! I think the short answer to this is I've always been really fast at doing things? I used to do NaNoWriMo, starting in 2013, and I've done 10k writing days before, so I think I've just built up naturally to being able to write a lot in a short amount of time due to practice (although I definitely can't sustain that speed for longer projects). For the secret code, I used to make them up all the time as a kid! So it's kind of also second nature to make them, and years of practice made it easy to throw together.
For everything else, I just kept the art simple. Collaging the backgrounds was fairly quick, and I also have built up free stock images/websites over the years to pull from lol, and I kept the sprites and GUI pretty simple! I think the longest and hardest part for me was the coding, since it's the skill I use and practice the least.
I guess tl;dr is I have years of practice at being quick at things, specifically!