I've killed a few 250 - 300 lb hogs. Taking them down clean with 1 shot is DANG tough. Now these are nice tame hogs in a 15x15 foot pen. Even then getting the right shot takes time, patience and a bit of luck.
Hogs have a big head, but a fairly small brain, so you draw an imaginary line from one eye to the opposite ear. Where those 2 lines cross is your aiming point for a head shot. But, if the pig in question raises or lowers his head as you shoot, chances are your going to miss the brain and just lodge a bullet in the bone of his skull. And of course that pig is not going to hold still so you can shoot it again, so now you have a very ticked off rapidly moving target.
Multiply that x 3 for hogzilla and your up to 300 mag's or elephant guns if you want it done right. They are simply lucky that the big sucker ran instead of charging the guns.
What was this one eating? The original Hogzilla was running around an area with several fish farming ponds. With fish food laying around in stacks for it to rummage through. Read virtually unlimited food supply.
So what was this porker munching on for it to get this big?
Its mother was almost surely domestic pig gone feral. Pigs go back to the wild quickly and easily, reverting easily to what they started out as. Long hair, tusks, and attitude are often seen in first generation feral pigs.
BTW the feral pig problem is becoming an ever bigger problem nationwide.