Well
Spoilers
It seems to me like it’s a post-hoc creation. I remember just from the few episodes I watched that the characters already had a desire to build a rocket and go to space. This seems to me like they came up with this idea of the mystery on the moon to create a justification for creating that rocket.
You can sort of tell that the writer just wanted to show people building from stone age to space flight in one shot, and that any plot around it is just a construct to have reasonable motivation for the characters to do exactly that. I wonder if they were inspired by games like Minecraft, Don’t Starve, etc.