Okay, so this is just a duel map sample that I started up in the modern age.
But I did notice something this time - in the loading screen at the beginning of the game, where it lists all the game's enabled options, it actually says "No Future Era" is enabled - even though when I get into the game itself and enter the worldbuilder, the "No Future Era" option is unchecked! I didn't notice it before because I had been playing around with all sorts of options, this time, I left all the options unchecked. (Also, the game seems to start in approximately 50000 AD, didn't notice that before, not sure if that's a bug.)