A garbage disposal is really a very basic design. There is a rotating wheel attached to the top of the motor shaft with ridges on the outer surface of that wheel that grind the material as it passes between the outer edge of the wheel and the inner wall of the disposal body. When they disposal is clear there is no physical contact between the grinder wheel and the body, so the motor shaft should turn totally free without any noticable resistance.
It sounds as if you were able to free the locked rotor condition but perhaps whatever was locking it is still in the machine,
Make sure the disposal is turned off, then using a flashlight, push back the rubber flappers and examine the outer edges of the wheel to see if there is any hard object such as a bone, bit of plastic or a metal soda can tab still in the machine, If you see anything in the groove use a pair of needle nose pliers to pull it out.
