Older Style Grounded Power Cord
Yes this is the original style grounded power cord, you replaced the outlet cover screw with one that came with the appliance that had a post sticking out and you connected the loose wire on it and then plugged in the DW, I don't thing that this system was in use very long as by 1959 the current style three pronged style cords appeared on washers and portable DWs. I think that all outlets in new homes were the grounded style by about 1962, refrigerators did not get grounded cords till about 1969.