Help me understand here.

I see nothing wrong with the question. Now, if he was breaking down, etc. etc. etc, then it MIGHT be inappropiate. However, your description sounds that that is not the case. My guess is he was really upset inside for some reason or another, and was looking for a reaosn to blow off some steam (whether it be directly related to the matter at hand or something else he is frustrated with in which he latched on his feelings from that topic to the one you were talking about).

I would advise as others have said-give him some time. Let him calm down, and then calmly discuss with him how you feel. If he gets upset, then that is fine, you talked with him in a civil manner, and he doesn't want to deal with it. Of course, if you HAVE done this already, and he STILL does this, it may be time to gently distance yourself from him. Be there as a friend and lending ear, but such that he must take a bit of the effort, and hopefully find the value of your friendship.

Jam it back in, in the dark.