RTF is a global modification that replaces all towns in the game.

I think it can still be integrated into the original lore. Ranged weapons already exist among the gremlins (arquebuses); it can be linked to that. For example:

To improve their hunting, the northern peoples decided to use more advanced weapons. With the diligence characteristic of dwarves, they improved the mages' arquebuses, equipping the rifles with an elongated barrel and a larger charge of gunpowder. Armed with such weapons, dwarf hunters are capable of piercing any armor, but not at a very long distance.

To make an accurate shot from that angle 😉