Take a car and attach a plow behind it to cultivate a field then the car becomes a tractor. Hitch up a team of horses to a car and pull it around, then the car becomes a wagon. Cut off the top and remove the back seat and trunk lid, then the car becomes a pickup truck.
So it is with the fly. Cast it with a fly line then the fly is a fly. Cast it with a spinning outfit then the fly becomes a lure.
I have seen flies that I called lures and a few lures I called flies. So, I feel it is simply how you cast them. Then again????????