How can these two motors produce the same torque if their volt/amp ratings are different and their watts/RPM are the same
P=IV and that gives 640W for both.
If the designs are different ie number of windings etc then the voltage can be changed for a different current while delivering the same power at a given speed.
Now power = Force * distance * time
So, the torque is related to power.
For a long explanation, see:
http://www.epi-eng.com/piston_engine_technology/power_and_torque.htm
especially at the bottom of the page.