Didn't Harry see him with his sight? Wasn't it a Hellboy like sight?
demony yes, but we cant read much into that since Murphy is as much an Angel.
All it says is that he made a choice. Not what choice he made, or the conditions of the options.
My mistake, I though the WOJ is where it was stated he was something else, but I was definitely wrong on that. Might have actually been in BR, from McCoy (which a less reliable source for sure)