Yeah, I've seen that one. I thought the TSN actually popped out of a rupture on the side of the Gulper? Makes a person wonder how many of them explode in nature when they try the same thing. The ability of Gulpers to do stuff like that is well-known and well-documented, so most of the time when a Gulper eats a tankmate I think it is still the owner's fault. The other fish is lost not due to a sadistic desire to watch live feedings, but rather due to a simple lack of research on the part of the owner.
But, admittedly, Gulpers seem to be able to surprise even people who "know better", simply because their swallowing abilities are just so extreme they are literally beyond belief. I can't really say that I hold that against them; they look like little comic-book caricatures of typical catfish, so I still kinda like them. They're so ugly they're cute.