Yes, the metaphor is quite vivid and gets the point across maybe even a little too clearly: if you see the shadow, you do know there is a moth casting it. If you hear a story, you may still believe it's entirely made-up or a result of some confusion. Then, still, this would create the impression of the protagonist's conviction that yes, the stone is true and the persistence of the story is the proof (the matter whether the conviction is correct aside, that's a vivid image of a personal hunch.)
On an unrelated note...
In "The Plague" by Albert Camus, there's a character, Joseph Grand. He writes a novel. He wants the novel to be absolutely perfect - he wants it to be so great the publisher would say "Hats off, gentlemen!" the day he reads the book. Grand spent years writing that book. He got as far as:
One fine morning in the month of May an elegant young horsewoman might have been riding a handsome sorrel mare along the flowery avenues of the Bois de Boulogne.
He never got past polishing that first sentence and making it as perfect as he could. When the book ends, he's still polishing that single sentence.
How long have you been writing about that Flying Stone by now?
