Well it's definitely not story related on the same level as Morrigan in DA:O. But either way, I still think that it's story related the same as everything else.
It does make some sense where it's thrown into the story too with the camp celebration, everyone is kinda letting loose. So if it was going to happen at any point it makes sense that it happens then.
Well, I don't think that if you knew nothing of Morrigan's character beyond the point of the sex scene in camp you would necessarily think so highly of her character.
