Have you heard of the Hogzilla? In a nutshell, a guy killed a giant pig (or so he said). He took a picture of it. Then he buried it.
Some people figured the famous photo was fake. The pig was just too big. Later, scientist exhumed the thing and determined Hogzilla was real. The story behind Hogzilla, and the guess as to how he got so big, was interesting and believable.
Now there's Jowlzilla.
My guess: that jowl isn't cut the way people normally cut jowls off a pig. We've killed the same pigs* and at 280#, and I don't think they have jowls that heavy.
Some butchers cut jowls in such a way that some of the shoulder winds up attached to the jowl. When they do that, the jowl will be heavier and the shoulder lighter. I'm guessing that that's the explanation for Jowlzilla.