Don't know who in Giant said that, but both points could be correct:
1- If you pedal in a low cadence with hard gears it means more stress for the motor, which means that your way to pedal could produce overheating.
2-Is not normal that "easy" overheating for this type of bike, and stoping assit with an error is not the best way to deal with. So Giant realize about it, get the feedback and will improve the way to solve with an update.
For this update the assist won't stop, but the performance will be reduced to reduce the stress on the motor to aboid the overheating.