As DallasStripes alludes, it depends on the nature of the action. If he turns toward the NZ like he is starting to move downfield to run a route or seek an opponent to block, but before the ball is snapped, then that is a false start - just the same as a tackle charging forward.
On the other hand, if his motion is smooth, more like he could be simply changing positions - and he is just moving forward at the snap, that would just be illegal motion.
If in question, FST is the safe call.
