Lua documentation focuses solely on the differences between tables and the things they replace...
It took a lot of reading, testing, looking up others' source code and a dash of frustration, but, with help from Pico8 community, I managed to (at least partially) wrap my head around it. The moment it finally clicked felt awesome!
To make it easier on myself, I wrote this randomized enemy spawner as a new program, away from my game code. I used simple placeholders for most of the elements. That way, nothing else would come in the way of grasping this concept. I think it paid off, because I got it to work and even made some pretty clean looking code:
Edit: I was advised to change the table o from the create_bug function to local table to avoid other functions grabbing this data when they don't need to. I changed that in the code below.
There are still some small things I do not know exactly why they work, but I know how to make them work, so that's good enough for now. I will continue expanding this code to make those enemies move and possibly not overlay each other, then I can transplant it into the game proper. I hope that by doing so I will figure out the bits I don't fully comprehend.