A Nephalem is the offspring of an angel and demon. Every angel, demon, monster, or anything else is very well-aware of what a Nephalem is and why they are deceiving by one. You are one, and since you were little you have remained hidden from everyone's radar. Until Castiel finds you. His look was filled with fear. But you read his mind, he thought you were worse than an abomination. In silence, they both stay like that for a while. He is still standing, not knowing how to introduce what he wanted to say.