Of course he grabbed Lucifer the moment that he sank, pulling him up out of the mud and staring at Dean for a moment, just sort of lost on what to do.

Lucifer was helping them. Lucifer said he owed Sam. He wasn't sure how to feel about all this.

So he just grabbed the archangel, hauling him to the backseat and getting him in the car as best as he could, sliding in next to him instead of getting back in the front seat.