Yes that's more or less it from what I gather. The trim cutout is designed to stop runaway from due to failure of the motor control circuit. Some ommon failure modes leaves the output stuck on. The only fix is to kill the power.

However if you kill the power to the trim motor and then turn it back on MCAS will blindly add more trim on top of the trim it previously added. It doesn't remember how much trim it's already applied.