If you try to create a superflat world with a custom preset code, Minecraft spawns villages in that world, whether you have specified the "village" tag or not. This is fairly easy to reproduce:

1. Create a new world with a custom preset code, for example:

3;minecraft:bedrock,61*minecraft:iron_block;1

2. Execute the following command:

/tp @p @e[type=Villager,c=1]

3. You will get teleported to the nearest village in the world.