Li Ling was actually quite angry inside since he was still a young man who had strong emotions, but had gained strong control over them after all he had been through. However, control over one's emotions did not mean that one did not have them or did not feel them, only that one did not let them affect one's actions without intent.
If you slapped Li Ling, he would still feel angry, but he would not show it on his face if he did not want to, and he also would not lash back with a retaliatory slap if he did not want to. He had this basic control over himself, which differentiated him from a mere beast.
Even when he killed, he did not do it out of emotion, but due to cold calculation that he could make the kill and get away with it. Even during his impulsive phase, when he vented his true nature after being given free rein and a taste of power, he still chose to go high risk, high reward rather than pure recklessness.
