Emma can't stop her curiosity as she wondered how this man blocked the attack despite the fact that they have huge differences in their levels. In order to figure out if Ling was stating the fact, she has to fight him. Well, she was well informed that this man was so skilled to the point that she should not lower her guard no matter what. Otherwise, she will be ended up getting defeated.
Moreover, Ling can't afford to die from her attacks, that's why he raised his guard and prepared for the possible attacks that will come at him sooner or later.
Swoosh!
To not receive any fatal damage at the very beginning of their battle, he has to hide his existence from the darkness. By doing that, he can conceal his presence from her, at the same time, increase his stats in just a blink of an eye. In his mind, he was so lucky to play this game at night since his passive skill was getting useful, that's why.