From the information he had on Kim Shin, he knew Young Jae was the other's flatmate. His logic made sense, and he realised that Dusk had always been a quiet one and a responsible soul. He felt guilty for judging Young Jae for the first time in the evening. After all, he owed both Dawn and Dusk for the help they did a few months back.
Wang Chul remembered Young Jae revealed nothing about himself to others until the fateful day. He revealed the pain of being different in the entire family and being hated for it without revealing the details. Wang Chul looked at Young Jae and connected all the dots.
Even though Wang Chul won't reveal the pieces of information to Wang Min Jun, he realised that both of them were bound to be with each other. Or else how in the seven hells did Young Jae saved Min Jun long back from pain and suffering. He even prevented Min Jun from being ended up in a messy situation. Only if he intervened long back, maybe these two might have been together.
