I think the dad slapped him because bittu called him soft and kind hearted and he did this to show bittu that he isn't that soft. I don't think it will end up being a serious scene for some reason, a lot of the precaps have shown something and you can a presumation that turns out to be something completely different so it's possible this is a similar thing
He gets slapped and then the dad makes a joke of it and says that ' see I'm not that soft and kind hearted'. I am probably completely wrong but this thought just popped into my head