Possibly it's one of those flies that just has the "right" characteristics to imitate a variety of things. What we see these flies as really doesn't matter, it's what the fish mistake them to be.
I've used many flies that were supposed to be a specific imitation of something, but in my own twisted way, have imagined them as something else. I've also used flies that didn't imitate anything that I could really think of at the time but may have used them in a manner that imitated something real. Call it abstract thinking if you like, but I prefer to call it open minded.
One of our greatest fallacies is we too often think of flies in our own terms. We define what they're supposed to be by what we see. Fish don't think, they act on instincts & conditioning from their environment. Really doesn't matter what the fish see when they spot our fly, as long as they see it as food, or as something else they have to bite at.
Food & self preservation is what fish are interested in. They don't even appreciate the art
How about a Meat Whistle, or an Intruder? How many different things do they imitate?