Why does Ythril spawn archer militia?

Playing an Ythril campaign and one of my cities gets attacked. I have some defenders and, as usual, a group of militia spawns. In that group however, there are archers! For Ythril. You know, those guys who don't have any ranged weapons!

This breaks the uniqueness of the factions and pulls you right out of your immersion. I have painstakingly nursed an archer-unit I've gained through a quest and now, out of nowhere, I learn that my faction can, after all, learn how to shoot a bow.