Something interesting to note, indigenous Australians also had a very high protein diet, consisting mainly of meat, with some yams, seeds and fruits. One of the ways in which they obtained adequate vitamin C, was from eating the intestinal contents of grass eating animals, such as kangaroos. Not all tribal groups did this, but many desert people did, because the vegetable content of their diet was so low.
They probably learned this form observing wild animals, which often do this. For example wild wolves will go after the guts of the animal they killed first for the plant material being digested in their systems. Then they go after the muscle tissue.