People usually chose to remain silent when they were angry. It could be said that they were too angry to say a word, which was why they usually opted to stay silent for the time being until their anger subsided.
Yu Ming thought that the case was the same when the demons standing in front of him remained silent after his apology. When people fell silent after hearing someone's apology, they likely didn't like the apology, right? That's why he expected the worst when nothing came out of the demons' lips.
Even when Bolin suddenly let out a heavy sigh, he thought it was a bad sign, and he prepared himself in case the silver demon confirmed that he was indeed angry.
