Hernias can happen after castration even without a cut pig being ridden. Sometimes it happens right when you're cutting them.
You gotta act quick when that happens. If you have some hog rings and a hog ringer, you can shove the guts back in and staple the cut shut. That usually works. Or, you could call the vet and have come out and put the guts back in and sew him up.
I wouldn't let him walk around like that. He could more than likely end up a dead pig.
I'm sure that most people probably think 100 lbs. is too big to cut a pig, but that's not so. I've cut 300 lb. boars, but they get set back more the bigger they are when you cut them. We used to wait until the pigs were about 120 lbs. to cut them, then we started cutting 'em at about 80 lbs. and we finally wised up and started cutting them around 4 weeks, before they were weaned. It's a lot easier. We'd put a piece of plywood on top of the farrowing crate and set him on that plywood on his side. Your catcher would hold the pig's up hind leg with one hand and can take the other to hold his front shoulder and hold his mouth shut, so you don't hear squealing all day long. Cutting pigs is actually easier than most people think; my Dad cut 5 Hamp boars (60 lbs.) blindfolded on a bet from a Moormans feed salesman that was at our place. Took him a little over two minutes, as there were two of us catching . With the bigger boars, you put em on their side on the ground and hold their hind legs with hand and put your knee on their front shoulder. For the big boars, we had a catch crate and cut em standing up. If they tried to back up, a cable loop in front of their hind legs would lift em up.
Let us know how this pig does, but I'd try to get him sewn up quick.