Not being ruminants, swine don’t normally eat all that much forage. While this makes a great story, I’m just a little suspicious of its complete veracity.
Most pig farmers who raise pigs full-time have feed mills and grind their own concentrate feed (mostly corn + soy etc). It may be that he puts this stuff in his mill and mixes it with corn, soy, and other stuff.
By the way, pigs will graze alfalfa. Pigs will eat almost anything. I well remember walking into a pig barn in Denmark during a trip there. I saw a bit of movement at the edge of a sheet of plywood that was leaning up against the wall, and moved the top edge back to look behind it. There were about a half-dozen large rats hiding behind that sheet of plywood. When I moved the sheet they all went scurrying into the hog stanchions. The hogs got all excited and pounced on the rats just like cats or foxes would do...pinning them to the floor with their front hooves. The hogs then gulped down the rats as if they were twinkies.
Hogs love snakes (almost better than any other food) and will slurp them down in a heartbeat.