The "butterfly effect" is a theory. According to this theory, when a butterfly moves its wings at one end of the world, it can cause a tornado on the other side of the world. -> something small (a butterfly) causes something big (a tornado).
But "Anne of Green Gables" is an old book (1908). And the "butterfly effect" is a new theory (1972). Therefore, a sentence from "Anne of Green Gables" cannot refer to the "butterfly effect".