Without reading the studies I can't say anything at all, seems like a baseless assertion to me.
Brain storm: which proteins do they mean? The proteins in beef or are they talking about gluten and casein. Gluten and cow casein are horrible allergenic junk but they come from grains and dairy which we eschew. It would be dishonest to take a study that uses those two and try to extrapolate that to animal protein which has been deeply entrenched in our genetics for millions of years whereas gluten and casein are within the least 10000.
Animal fat? Arachidonic acid. That is why we stress low omega 6 meats that are fed grass and have adequate omega 3. That doesn't mean not to eat animal fat, it means eat more grass-fed beef and less chicken, take fish oil, eat fish, etc. It's all a delicate balance.
Stabbing conventional wisdom in its face.
Anyone who wants to talk nutrition should PM me!