That...was not actually very helpful. What even, Castiel. Though he does get a couple of points for recognizing that Kurt is male. That should bring Castiel's total up to, oh, about -32984 or so. Give or take.

"An opera is a type of play," Kurt cuts in, even though Dean brought it up. He doesn't trust Dean to try and explain opera, and witnessing it would probably be painful. "It combines drama with music. It's typically associated with very high, classically trained voices, though there other ranges incorporated as well. It's also extremely high class."

In other words, it's a huge compliment. He'd rather be told he could sing opera than told he's an angel any day. You could say his smile is a little more genuine, but it's honestly only because he's preening a bit.