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He was simply stating his opinion that people ask "How are you doing?" without necessarily wanting to know the real answer. Most people answer that question with the word "Fine" even if their life is turning to cr*p around them! Most people don't really consider that someone is asking after their health or wellbeing. Saying "How are you?" or "How ya doin'?" is frequently just something to say after "Hi" or "Hello". Sometimes we don't even expect an answer.
Your friend is not saying necessarily that he's not fine. He's saying that he won't say he's fine if he's not.
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