I can't see Castiel confess to letting Sam out either. And now with the Apocalypse over I doubt they'll bring it up again on the show. Which is a shame, really.

I think Dean does suspect that it was an angel who broke Sam out. But without the sigils carved into their ribs it's not impossible that another angel found them and did it. But Dean must as least have considered Cas.

Thank you, I'm glad you enjoyed it.