The point of that analogy is that no significant change has to be made in order to create a new timeline. Merely "stepping on the wrong bug" can cause changes in history thanks to the butterfly effect.
Someone coming from the future into the past would create absolutely
massive changes in history, even if they came, did nothing and left. New atoms are added in the universe by their mere presence which wasn't supposed to happen. Like it or not, that is going to create butterfly effect down the line. It might take years to become something significant, but it will happen eventually. Look up the
infinite monkey theorem.