It was precisely because he was so certain of the situation that the Domain expert wielding the sword believed Zhou Tian was definitely dead after decapitating him, and it was for this reason that he finally let down his guard. He didn't anticipate that his own complacency in that moment would directly lead to his death.
In ordinary circumstances, indeed, Zhou Tian would have been dead. The head is an organ even more vital than the heart, and given Zhou Tian's current realm, he had no way to negate the function of the head. Thus, decapitation equated to death. In that situation, the Domain expert's response could not be considered incorrect.
However, no matter how much that Domain expert thought he knew about Zhou Tian, what he knew was merely some superficial information. In truth, the things about Zhou Tian that could truly be considered important were definitely beyond the Domain expert's understanding.
