In a pre-gunpowder society, one does not “fire” a bow. One can shoot a bow, but one cannot fire a bow.
The only time a commander would order his archers to “fire” their bows was if he actually wished the archers to light their bows on fire. This was impractical, and, as you might expect, rarely happened.
The term “fire” refers to lighting the gunpowder of a firearm on, well, fire.
As even Guy Gavriel Kay fell into this misuse for Under Heaven, I felt the point might bear repeating.
Postscript: Also, it appears I have used my 100th post on this blog to make this complaint. Huh.