Master Ju had been directly facing Qi Tian the entire time, leaving his back undefended. He never expected the attack to come from his two companions behind him. While it wasn't a lethal attack, it disrupted his rhythm at the crucial moment when he and Qi Tian were engaged in combat.
Master Ju was thrown off balance by the attack. He had been remotely controlling the Whip Wind, a powerful force that was not easy to control and required his full concentration. Any minor lapse could lead to complications. Unfortunately, that's exactly what happened. His distraction caused his control over the Whip Wind to weaken significantly.
