That claim is as real then as it is now. Forging alters the crystal structure of metal and the boundaries in the metal. It makes it significantly stronger in one direction at a slight loss typically at 90 degrees to the crystal structure. It is the goal of forging steel (and a few other metals). There is a test used in forged material referred to as a 'notch test.' A thin section has a notch made using harder material. The edges of the notch vary depending on the direction of the metal boundaries at that point.