He's probably just mature and well-rounded. I would say I'm pretty warm and sensitive. I'd also echo the statements about familiar people. To outsiders, I'm closed off. He's probably a lot warmer with close family and friends.
Also, the older I find I've got, the more I accept that I'm not a genius or anything like that, which I used to think as a kid. This may explain why your dad is a little more cautious in his abilities - life experience. Compared to a lot of other INTJs, I seem to be a lot less confident, so I don't think the 'fear' that you describe is that unusual.