Why? I think (I didn't analyze anything) that is because I'm just being myself. I talk to the interviewer like it's a friend. If I think of a joke I just say it. Thoughts like "will be it ok if", "should I say this or that", etc NEVER cross my mind. I'm having a conversation, not a test. Same for technical stuff, if I don't know something I just say I don't know. Hopefully I still have an idea, so I would say something like "I don't know this / never used that, but my first guess would be X", then usually it ends up being a discussion that at the very last would teach me something, even if I don't get the job.
That being said, I understand it's hard to do stuff like that if this is not your default mindset and you are being close to desperate.
Still... he is not stupid, he will not go bananas. I think there will be economic growth in America. Hopefully less corruption and no terrorism. Look at Europe... they have the "open mindset" approach and there are more problems there than anywhere in the world (regarding politics, terrorism and common people not being happy)