Looks as big as a steer that weighs twice as much.
Weight looks reasonable, but I wonder how they propped him up, with head up. Must have waited until rigor set in, is the only way.
The photographer used a little perspective sleight-of-hand.
The hog is a lot closer to the camera than the hunter, who is a couple of feet behind the hog. At first glance you think he's propping his arms on its back, but he's not.
This makes the hunter look smaller in comparison to the hog than he really is.
I think that the hunter was well behind the hog, distorting your perspective.
Yeah, it's an old hunter's (and fisherman's) trick to make an animal look bigger. You just position the hunter at least several feet behind the carcass instead of right behind it. The lens does the rest.
It's all in the photo position. Place the hunter about ten feet behind the pig and it makes the pig look much bigger, like around 850 lb.
If the hunter were next to the pig, the pig would shrink to the size of a 55 gallon drum, around 480 lb.
To understand, think of the fisherman who holds a fish out in front of him at an arm's length, and has a photo snapped. It makes the small fish look huge.