You have ran out of arrows

Maybe bowman/corsair skills don't actually have programmed into them what kind of projectile they use, but it's determined by the weapon being equipped (which would make sense). You got dispelled the same instant you hit an attack, so it tried executing the attack, but you didn't have the gun anymore so it reverted to default and consumed an arrow. Or would have.

That doesn't explain why it didn't say U NO HAZ WEPUN though.