That's the point. Players have gotten round that by feinting their strike at a point whereby they can dummy the keeper into committing, then changing the direction to the vacated space.
It's considered foul play to stop, re start the run up and then do it.
I THINK that is the way it's intended. The rule isn't unequivocal in the laws of the game, but that is the illegal feinting mentioned in rule 14, I believe.
“feinting to kick the ball once the kicker has completed the run-up (feinting in the run-up is permitted); the referee cautions the kicker”
The only question is whether Son had completed his run up. In my opinion he hadn’t, others see it differently. Ah well.