At the time this postal card was sent to Canada, the 1-Cent rate for merchandise samples of 2 ounces or less was the same as the post card special treaty rate. The big evidence that considers the former is the "Customs/Duty Free" marking applied by the Canadian officials at London, Ontario.
The backside of the card exhibits a "sample" of a large machine tool. Perhaps this illustration prompted Canadian postal officials to consult the UPU regulations regarding merchandise samples, ultimately judging the card "duty free".
Place mouse on image to see the reverse side of the card.