The umpire is calling fault 13.4.4 in the laws of badminton.
“obstructs an opponent, ie prevents an opponent from making a legal stroke where the shuttle is followed over the net.”
The shuttle is close to the net. As long as Ginting hits the shuttle on his side, he is allowed to follow through with his swing over the net, and should not be obstructed in doing so by Christie. The umpire judged that Christies racket was too close, obstructing Ginting from following through over the net.
The commentator didn’t agree with the call, and neither do I…
But for example, if their rackets had collided in this situation, then it’s a clear fault for Christie, since a racket collision is indisputable evidence that he obstructed Ginting’s stroke.