If Castiel looked saddened over the fact that he was (again) someone that Dean did not recognize, it was only for the merest of instances. He was becoming accustomed to the idea of people coming here from different times, different realities. And if Dean had been truthful about being a demon (which Castiel knew he was -- he was an angel after all, and it wasn't difficult for him to sense demonic or supernatural creatures in the slightest), it could only be assumed that this particular Dean Winchester had never been raised from hell.
It was a strange thought -- that somewhere, there was possibly a Castiel who had never gone to hell and seen the utter beauty that was the light of the Righteous Man's soul, even in the deepest and darkest of places.
He moved -- careful and controlled, pulling out a chair across from Dean's seat and settling himself into it. He sat stiffly, back straight and shoulders squared, like he saw no reason for comfort or relaxing. "I am an angel of the Lord," he agreed, tilting his head thoughtfully and squinting at Dean. Not his Dean, he had to remind himself. "I have no mission to dispose of you, although I suppose it would be wise to warn you that I would do so without regret if the need arose." A lie, but not completely. "My name is Castiel, and I know more than just your name."