Luo Cheng was influential enough in the Beijing area to have heard rumors, as well as gained some evidence regarding the existence of Horde Kings. But until now, he had never met one. I mean it was a secret kept by the highest ranking members of humanity and its many factions that had emerged out of the Apocalypse.
Beijing was home to a Tier V Horde King. And he and his Divine Sword Sect would need to go out into the countryside if they wanted to clash with a Horde King that they were capable of surviving against.
Something which naturally he had not done. But that did not mean he was not aware of Horde Kings and how terrifying they could be. I mean, with the evolution of humans it wasn't like Horde Kings had stayed stagnant.
Especially with the evolution of mutated beasts as well. Horde Kings could gain strength by consuming awakened humans, which by now was pretty much the only variant that remained outside of isolated groups like the Remnant.