Spoilers Skin Game - Surrender

So I'm relistening to Skin Game and just got to the part where Nicodemus surrenders but Karen tries to strike him down and the sword goes dark. However, he really didn't surrender so I don't get why the sword goes dark.

The Genosqua is essentially a tool of Nicodemus and he did not put it aside. He says "I surrender" but obviously didnt. Has Butcher ever explained the inconsistency?