Good day,
Phatic communion 'questions' like 'how are you?', 'have you eaten?' or 'where are you going to (pergi mana)?' serve to establish some kind of social link between people. The 'correct' answer then is one which is acceptable (either grammatically or substantively) to both sides.
All 'correct' answers then are the the result of being 'impressionable', i.e. being in sync with the social context in which they are made. 'I'm good' is more in sync with the English more commonly used today while 'very well, thanks' with the time I was taught to respond to such questions.
Substantively inappropriate responses are far more interesting. I once heard in response to 'how are you?', details of someone's home and work life, and a suggestion at the end that I was a busybody.
Cheers.