I love a good email or note - because it's not something you thought out to cut him down. He said something as part of a silly game you were both playing, and you said something defensive back. It's probably not a good type game (for anyone) to play with him, talking about families when that's a shitty area of his life. Everyone gets defensive about family. But it's going to go wrong for him pretty frequently unless the other person is willing to to have their family slagged and not say anything.