Chen Fangli assassinated a cultivator from the Zhou Family. Whether it was to vent personal grievances or to help the Chen Family attack the Zhou Family, this wasn't the main point for Zhouyang.
As the Zhou Family Patriarch and a Foundation Establishment Stage cultivator of the Zhou Family, he had the responsibility to protect the weaker members of his clan.
A Qi Cultivation Stage cultivator from the Zhou Family met an unjust death at the hands of Chen Fangli. For this reason alone, it was enough for him to kill Chen Fangli to avenge the deceased Zhou Yuanjing.
However, before killing him, he had to do one more thing, force Chen Fangli to confess.
He saw Zhouyang reach out and tap his storage bag, pulling out two Memory Pearl magical artifacts, which he hid after activating, and then used a "Soul Calming Technique" on the unconscious Chen Fangli. This helped him barely calm his chaotic mind, allowing him to wake up a bit faster.
