There's a bug with either Chung Mu's DWTs or Zao's protection system. Someone in NA server made a thread about how his DWTs hit a practically full HP Zao for 600-ish damage and 1 flood. The Chung Mu player uploaded a replay and his concern is actually valid. Even better, the Zao player he hit posted up a replay and even a Youtube video so you saw the exact same sequence from his view. Here's the Zao's moment when she got hit by the DWT for practically nothing.

https://youtu.be/CoxDUyJUOkw?t=17