I didn't play the divinity games, but what you wrote there resonates with the caption on this board : "In the silence of a godless age, the faithful are cleansing the world in the hopes of reclaiming divine favour. But from the embers something unseen begins to awaken."
So do you think they picked the wrong guy to sacrifice or that their ritual was noticed by a different being than they hoped for? Or maybe that they didn't really know whom they were sacrificing to? Or maybe it had something to do with the central dwarven character who becomes the centerpiece of the ... thing?