Before this, Melgor was somewhat aware Ren Xiaosu had been hiding his strength. However, he wasn't clear just how much he was hiding.
One's imagination was limited by their horizons. As such, Melgor thought that even though Ren Xiaosu was hiding his strength, it shouldn't be by too much.
But after this incident, Melgor thought he was mistaken. He was far, far mistaken.
In the entirety of the relay station, he was the only one who really knew everything that happened.
Ren Xiaosu was not in cahoots with that bothersome Wang Congyang at all. It should have been a spur-of-the-moment decision by his steward to create chaos while he was pursuing his enemy.