No. He's treating him better because the MC is "behaving" (read: doing whatever he says and staying confined to his house and never saying no) But he is at heart, an abuser. He'll find another reason to abuse the MC eventually
Yes this is part of the extra chapters in the novel, he becomes more attentive overall towards mc. In the novel mc increasingly starts to trust him with normal yapping, treating him as a normal boyfriend (like this one of calling him to ask for ice cream randomly) and Kangwoo started to adore that, so he tries to avoid scaring him when he gets mad about something, because he doesn't want mc to sulk and be closed off and wary of him as before, he likes the boyfriend treatment
Okay, or am I completely confused about what's going on there, or has Seme started to treat Uke more attentively, with a desire to do good to him not only from the point of view of "I know better and I'm a control freak", but from the point of view of a more careful attitude towards him? Hmm... well, okay.