You expected him to say "no" to the "stupid" bet, and "yes" to the $50k bet. I'm not sure I follow your logic.
I would have been surprised if he hadn't accepted the "stupid" bet, because it seemed to me that he truly believed that whole Q white-hat military narrative. I would have been very surprised if he had taken the $50k bet though, because nobody could be $50k sure about a future event, and nobody would ever believe the other person wouldn't automatically welch - making it a pointless bet. My impression of David is that he is an honorable person, and that is my impression of you as well. I have no way of knowing, of course, but I'd like to think that David would pay whatever amount he agreed to pay.