Not necessarily, you could have a gate at the very end that has to open up to let the signal through. There are inhibitory neurons throughout the nervous system, for example. It's also known that there is inhibitory circuitry that paralyses you while you are sleeping, so that you don't move while dreaming (see sleep paralysis for a common failure mode of this system). I have no ideas if motor signals do actually leave the brain when you are not moving though, it seems like an odd "design".
The inhibitory circuits exist in the brain and would prevent the motor cortex from sending out signals to the spinal cord. This device is reading motoneuron signals from the wrist when you are making movements. It's not mind-reading, the title is misleading.
