Well, there had been a rumor going around the previous day that someone was planning on asking if Dean was bisexual and if Dean/Cas was a thing, and they had been told by convention staff that it wasn't okay to ask Jensen, but it was okay to ask Misha. The crowd was really reacting in anticipation to what they thought the question was going to be. Which is still biphobic, I guess, but I want to give the full context.