It was actually a clever trick by the Allies, setting up a fake invasion force that made the Heer put more defence around Calais.
I remember when my Great Uncle walked onto the shore of Gold beach after the Canadian forces secured the area (He was FFF, they didn't do much initial fighting). He told me that he had met a Frenchman who had been conscripted into the Heer, and they he told them how surprised the Axis forces were.