FoodReference.com states that the English muffin is thought to have originated in the 10th or 11th century A.D. in Wales, while quick bread muffins originated in the United States in the 18th or 19th century. Quick breads are any baked goods leavened with chemicals instead of yeast.
American muffins, made in individual molds, could not have originated earlier because pearlash, a predecessor to baking powder, was not used in baking before the 18th century. Pearlash was first used for baking in the United States. The commercial development of baking powder only occurred in 1857. In contrast, English muffins are yeast-leavened and prepared using a griddle.