While I can't really say you did anything wrong, I would be kind of ticked off if I was him as well. From what I see you replied to his post yesterday evening, and then posted VERY early this morning that your parts were sold to someone else. That's hardly a reasonable amount of time to let him respond.
The buyer should have requested to be contacted via PM, and the seller should have contacted him via that method likewise.
It's probably just me but if someone goes through the trouble of posting a wanted listing, I at least want to give him first crack and give him a reasonable amount of time to get back to me.
Again, I don't think anyone did anything technically wrong, but it could have been handled a bit more respectfully. Live and learn I guess.
