Legend of Grimrock 2

Legend of Grimrock 2

Eye of the Atlantis
Knife thrower ammo botche?
Hey, just destroyed 7 knives in a fight be mere shooting.
They are nowhere to be found.
But the weapon says that this happens only during the Shrapnel Storm.
And I know that I haven't used one, because the prerequisite is Firearms 3 and I have only Firearms 1—just enough to use the normal attack.
So, what gives, is this a bug or just a typo or somthing else?