As I know, it's perfectly legal to extend your racket over the net and hit the ball if the ball bounces backwards over the net. And it's the only situation where you can actually cross the net plane with your racket to hit/return a ball. However, in this specific situation the returning player crossed physically the net plane. The ball bounced backwards close to one of the net posts and the returning player physically followed the ball to the other side of the net and hit it. Who's point is it?