The 570 oz-in rating would be a "holding torque", that is, the rotor should not rotate if a torque of 570 oz-in is applied. The holding torque is generally greater than the available torque when the motor is turning. The torque curve that you included in your post starts at 100 rpm, so the 0 rpm holding torque is not plotted.
If I did the conversion correctly, 570 oz-in is about 4.0 newton-meters. So it is not out of the question that that would be the holding torque of the motor for which the torque curve was given.