@Max well he did grow up in the slums where wearing his emotions on his sleeve was a bad thing. He has also had a traumatic life fighting for survival everyday in the slums. These things can desensitize you and make you appear emotionless. It's just a survival mechanism and something seen in PTSD patients. He also talks about how he is missing something that allows him to connect with people so maybe even a little bit of sociopathy going on here. He may be able to mimic emotion, but not feel it. Given where he grew up he never had to develop his mimicry of emotion skills.