Story says it was shot at a hunting club. Sadly, it's not uncommon for some clubs to buy them and let them go for their members to shoot. The fact that he shot it at 50 yards also points towards it being a pet at one time. Then there is the fact that it weighed 500 pounds, a weight very rare in wild hogs because they have to work for their food every day. Wild animals rarely get a lot bigger then the other wild animals of the same species. A little bigger, like 300 hundred or even 350 pounds is believable, but 500 is pushing it. Not impossible, but with everything else involved, unlikely.
Eddie