It's never mentioned again in canon, so presumably neither brother knows about it.
My head canon is that they both kind of know. Ruby couldn't have done it, and Cas had made it clear he was back on Team Heaven. But Cas was obviously acting under some degree of coercion, and he had a change of heart and died for them immediately afterward, so they decided to let it drop.
Another one for the list of things canon hasn't clearly shown that Dean/Sam know - I don't think Dean knows about Sam's very near miss with the truck in 7x16? It was never mentioned/discussed between them as far as I could tell.
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My head canon is that they both kind of know. Ruby couldn't have done it, and Cas had made it clear he was back on Team Heaven. But Cas was obviously acting under some degree of coercion, and he had a change of heart and died for them immediately afterward, so they decided to let it drop.
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