How does Jed use the fog to help the village?

Among the first things Ged learns how to do is how to cause fog. The fog he produces is so thick that he actually uses it once to protect the village from hostile raiders. In a subtle way, the narrator compares the fog Ged produces with the magic he possess and through this similarity he wants to point out that magic, just like fog, can be confusing and it can make people question the reality of the world they are living in.