Responses
Another thought, I think the reason why lee kang doesn't want the grandfather to be near the kid is because of how the sister and lee kang was brought up. Like I think they (grangpa) were strictly handling their studies and have high expectations to the point of making a math competition.
He may be just want his kid to be more free and have many choices instead of someone pushing their ideals onto the child.
I think lee kang is right with defending his daughter and it's not like he shouted nor harm the kid even though he is being rude ┑(￣Д ￣)┍ He even stated that he can approach his daughter again but in a better and polite way.
He may have been childish with the journal something but ╮(￣▽￣)╭ the kid's not nice.