We all love/hate/stare-aghast-at-the-unnatural-horror-of-a-world-gone-wrong when something without bones eats something that has bones.
Spiders that eat birds, water bugs that eat frogs, centipedes that eat mice (I looked for a link and got sick; I'm not too good around blood and guts)... they all suggest a strange terror of a world turned upside down, the "natural order" revealed for the chaotic sham it really is.
In short, invertebrates slaying and feasting on vertebrates is a whole other Horseman.
Clearly, some Horsemen are fuzzier than others.
I must admit, I don't really know what's happened here. I doubt a guy went fishing for worms and used a fish as bait, although the image is just too wonderful for me to shake. He picked up a cuddly little blighter, whatever happened!
It'd be different if it was a Bobbit Worm. They actually do kill and eat fish. So our precious nightmares of revolt among the "lower orders" are safe, not even worms will drop the ball on that one. And they don't even have arms.