I can accept the iron bolts being dense enough to go thru the dragons and not break but the bolt being dense is not what will make it go thru the dragon in the first place, the ballista is. Unless the author is trying to show us that this random office worker has deep enough knowledge about Nano-technology to casually make mono-molecular edges that will pierce thru literally anything regardless of what it's made of or how thick it is.
Though since we saw Kamshin lightly tap the one adventurers shield and cut it clean thru I guess Vans weapons have to be mono-molecular edged, meaning this isn't just Fantasy but Sci-fi as well.
(though we are working on mono-molecular tech so it may not be fiction forever.)