“You think I don’t know that you told him to try to kill me?”

“Yeah, I suppose that is how he would hear it. When I learned of the angel tablet, I did tell Castiel to get it at any cost.”

Because there’s a difference between being forced to do something that you don’t want to and simply calculate it as the easiest option. This is Dean’s face when Naomi hints that this last case was the anticipation of Castiel’s actions.