To be fair, I pity him. He was not at all expecting a child.
Korean society works differently and it's pretty much very normal to live with your parents until you marry. Children out of wedlock are not so much either. What he was not expecting was to go from 0 life responsibility to 100 with a small child.
However I think its better they choose to stay in Korea. No offence but if I was to choose to have a baby in USA or Korea I am definitely picking up Korea, no questions asked. He can find a job, social services there are really good and supportive for children, plus it's expected from woman to stay home anyway. Also kids learn languages very easily, the other one, 3 years old, is perfect age to start learning, she will learn in no time. Also his parents seem as awesome grandparents and huge help.
To be fair I was very surprised how many children out of wedlock and single mothers are there in USA. Or generally you guys have children waay too early, I mean having kids before 30 is not that usual in my country. Only when you live in small village the boring life. I feel like Korea is more traditional family oriented in this.