He could have had a hand in placing the curse to begin with. The "literal bloodthirst" being his idea. Maybe after Vova sired a shitload of vampires, Moiros changed his mind about the kid, and helped him in assassinating his father to make up for cursing him. And so the two have an understanding.

Incidentally, I still wouldn't mind some kind of Sun God to be Mikazliqui's mortal enemy.