The hook likes to ride 'upside down', so the bend of the hook helps the eyes flip the fly over. The bend also helps the fly to track a little straighter.
The Eagle Claw EC413, which is a jig hook the one used here, except instead of a 90 degree bend it's at an angle, is used quite a bit by striper fly fishers in the San Francisco/Northern Cal area. It's a very cool hook. For more info on this check out Dan Blanton's website.