narnian battles

The problem of crossbows

So throughout the PC movie, we see the Telmarines using crossbows.

And Miraz showed Doctor Cornelius an arrow when talking about the kings and queens of old. The arrow was used as proof of the existence of the Narnians. So what we have here is a clear dichotomy - the Narnians used to use arrows, and the Telmarines do not anymore. 

In the deleted scenes, we also see Susan using a bow and arrows, and Caspian a crossbow. Again, we have a perceptible contrast: the Narnians use bows and arrows, and the Telmarines use crossbows.

So the question is, who taught Edmund how to use a crossbow?