So Ive been looking at modern diets of both workmen and upper classes in where I am. I'm also doing research of how to cheaply meet the dietary requirements of strength training - and of course I wondered how did people back in the day eat to build muscle? How likely or unlikely a person to have a high muscle low fat build as what we can now achieve thanks to modern economy and health education.
I can't comment on how widespread the belief is among and between cultures - but an interesting example of the belief is given by Gandhi in his autobiography, The Story of My Experiments With Truth.
He recalls how as a teenager a Muslim friend convinced him to try eating meat, arguing that the reason India had been dominated by the British was because they were made stronger by their meat-eating diet. So even in a society where vegetarianism was practiced by a large number of people, the idea that meat promotes strength clearly existed and was appealing to most people.
The story might well be apocryphal but Gandhi was always writing for an audience and it probably indicates that this is something he heard people say often.
I don't know exactly what you mean by "lower tech cultures." I can tell you about Great Britain while it was industrializing. Around the mid-19th century the association between meat and strength was common within working class families as males consumed the vast majority of the meat at the expensive of their wives and children, who would acquire most of their calories through sugar and grain. There was this notion that he needed meat to perform his duties as the breadwinner.
The relationship between meat and strength also pops up in America. Wilbur Atwater (1844-1907) was an American chemist who discusses this idea in his Principles of Nutrition. He speaks to lean meat as a good source of protein, and protein itself as "fuel for the body." Nevertheless he states that a diet made up of protein would not be healthy and must be supplemented with fats and carbohydrates. A good example of this connection is America during the Second World War when rationing was fairly common; the country needed to focus its resources on the war effort. A significant amount of red meat in particular was sent overseas to fighting men because again, there was this belief that men would need this meat to maintain their strength and defend the homeland.
Sources:
Ken Albala - The Food History Reader
Sidney Mintz - Sweetness and Power