I think the post you were responding to tried selling the Idea that:
Kraagor, the dwarf, who we know next to nothing of + Serini, who at least at a time had a crush on a party member who was not called Kraagor = Belkar.
As such, Belkar would most likely not be related to any Black Dragons.
Just clarifying, not buying into that one until I see a beard on Belkar's face myself.