So I'm afraid that indeed, repeating crossbow justifications need very much apply.
I know they shot crossbow bolts, though this is the first time I've seen their exact placement on the weapon.
My statement regarding repeating crossbows is borne of this nonsensical logic many people have regarding firearms in high-fantasy settings. Metal-ball projectiles and exploding powder? The world is ending. Franchise over. Everything is ruined.
But... if it looks like a gun, handles like a gun, functions like a gun, is exceptionally more advanced than any early firearm, but shoots a crossbow bolt? The crisis is averted. The canon is saved (pun intentional). It doesn't matter if we're bordering on sci-fi tech, as long as we call the thing another thing, everything is good.
So the appearance of a crossbow bolt doesn't really change anything, save for the appeasement of certain individuals. In fact, the bolts being where they are makes even less sense. The only way I can envision these working would be the suspension and projection of bolts through some kind of Lyrium field... and that would make it more like some kind of magi-tech railgun.