I think of fraying as the fibers that make up the filaments of thread (or rope) coming unraveled, untwisted, pulled apart, not by being cut but by wear or stress. When I hit the hook point there is no fraying or tearing involved, the hook simply cuts straight through some or all of the thread filaments. Rough skin is most common cause of frayed thread, followed by rough tools. I always had trouble with rayon/acetate fraying, hated floss bodies because of it. The "flat" nylon threads that lay on like floss also fray from just touching them. Untwisting thread can cause fraying because the twist is what holds the fibers together to make a filament or the filament together to make a thread.
If the hook cuts only part of the filaments, those filaments may come untwisted or unraveled and eventually end up as being frayed.
My knowledge of the language though is as it was spoken/written in the mid-twentieth century and I have noticed that some words no longer carry the same meanings nor connotations that they once did. Perhaps this is another case of that sort.