This is written from an American point of view, and therefore reads as biased. The majority of scones made and sold in England, Scotland, Ireland are nor triangular, they are circular. Triangular scones where made by cooking a larger round scone and cutting it into four. The recipe originally used either sour buttermilk or sour milk. Modern recipes sometimes use a little yogurt or over souring agents instead. It did not include sugar or egg - it was a very basic cheap food designed to use up the leftover sour milk products.
American biscuit is based on scone recipes brought over with European settlers.
"What is certain is that the term is mainly a British one, and covers a wide range of small, fairly plain cakes. Leavened with baking powder, or bicarbonate of soda, and an acid ingredient such a sour milk, they are quickly made and best eaten hot with butter." ---Oxford Companion to Food, Alan Davidson [Oxford University Press:Oxford] 1999 (p. 704)