maybe they put the wheels on it in the usa.
"Screwdriver" assemblies don't qualify as being called "Assembled in USA" under the FTC regs... To wit:
"A product that includes foreign components may be called "Assembled in USA" without qualification when its principal assembly
takes place in the U.S. and the assembly is substantial. For the "assembly" claim to be valid, the product’s last "substantial transformation" also should have occurred in the U.S. That’s why a "screwdriver" assembly in the U.S. of foreign components into a final product at the end of the manufacturing process doesn’t usually qualify for the "Assembled in USA" claim."
In any case, the Canadian SO boxes I've seen said Canada on the label.