Figures the parallels would fly right over Dean's head, along with everything Cas had been trying to say. At least that hadn't changed. Joy.

Castiel doesn't have it in him to explain, so he moves on.

"I've been attempting to track the Leviathan as they move. I knew they'd been focusing on you and Sam specifically when I saw the bank robbery footage." Actually Cas had known before that, had just felt it in his gut and his...something, but that had cinched it. It was what had pushed him into really moving, rather than just drifting and surviving.