Difference between overload and short-circuit protection
Overload and short-circuit protection protect against two different parameters being exceeded: heat (power integrated over a relatively short time) and current. 

A high current can be a an almost instantaneous problem: a wire that can't shed its heat can get too hot and burn through, or set fire to surrounding materials. In a real short-circuit situation the voltage is ~ zero, so the power delivered by the supply is ~ zero.

Overload is a slightly longer-term situation, where the heat in the motor is the problem. A motor has much more heat capacity than a wire, so a peak is not an immediate problem, but over a slightly longer period the heat must still be limited.