I think he's confused; confusing herbavores, omnivores, and carnivores. And the swollen stomach bit - mostly humans on a high sugar / grain diet. Horses - preformance horses are completely grain fed and never have swollen stomachs. In fact, unless you can get them to overeat badly, none of them do. Of the other animals mentioned only the apes and gorillas tend to swell up when the gorge themselves.
As for fiber, IMO insoluble fiber is bad stuff. Soluble fiber in small amounts is quite sufficient.
"When the search for truth is confused with political advocacy, the pursuit of knowledge is reduced to the quest for power." - Alston Chase