I don't think the picture was photoshopped, It's an optical illusion. Film makers use it all the time, it's called "forced persective". In a current TV commeicial, the spokesman appears to standing by an enormous gas can. He walks toward the camera and we see that the can is normal sized. The same holds ture for the hogzilla pic. Notice how the hog is suspended closer to the camera and the person is standing in a hole farther away. That all works to make the hog look bigger than it actually was. (It still was a monster hog!)

I think the rest of the exaggeration can be attributed to the excitement of the moment.