The reason Tang Ye thought this way was because when he first encountered Xu Haishui, he claimed to be able to control zombies one level higher than himself. However, in the end, he couldn't even control Ah Fu, let alone Tang Ye himself.
But during the battle with the Zombie Dragon, Xu Haishui managed to use the power of a Level 4 zombie to control the dragon, and the current mysterious guy is also a mental zombie, but he couldn't handle himself.
However, that being said, the mental power of that guy could control humans, which was unheard of. The regular mental control zombies could only manipulate some power-type zombies to protect themselves. They had never directly taken control of another's body.