As the adult, I think Deukpal knows that he has to be the mature one between the two of them. If there is a fight, it's his job to mediate it. And he's aware that Sekyung has an agenda to get involved with him but to Deukpal, Sekyung is still just a kid. Sekyung has his whole life ahead of him and what kid needs to do is have a proper upbringing. Perhaps that's why Deukpal is trying to be understanding of Sekyung's situation.
As the adult, I think Deukpal knows that he has to be the mature one between the two of them. If there is a fight, it's his job to mediate it. And he's aware that Sekyung has an agenda to get involved with him but to Deukpal, Sekyung is still just a kid. Sekyung has his whole life ahead of him and what kid needs to do is have a proper upbringing. Perhaps that's why Deukpal is trying to be understanding of Sekyung's situation.