I have no clue what I did or how I did it, but I'm not going to complain by the end result. Just in case I'll go over every strategy I tried.

• Let the full cutscene playout, my theory is that villagers work during the cutscene
• Researched any tech I could find, that I could afford
• Built a whole bunch of obelisks, hoping that the god rays that it releases will increase the dig rate, like the Pharaoh
• tried helping the diggers using Arkantos's spear and the priest staff, maybe even kill the dirt?

Or it could be that the level starts with a random % completion sword and its just luck of the draw. Or even a extended edition change that's not present in the retail version of the game?