I see a lot of comments about how you shouldn't burn bridges. I agree, I still think this was right thing to do. I would excuse myself politely and walk out as well.

Maybe person should ask to talk to lead dev or whoever, explain him that he doesn't believe he would fit, thank him for opportunity and leave. In other words say, it's not you, it's me ;) and still leave and enjoy rest of the day.

I generally don't believe in daylong interviews, I don't see the point in multiple rounds, everyone on the team talking to you endlessly. It is a waste of everyone's time and energy, to me personally it shows how people are uncertain in their decisions and need support.

One more thing, this is opportunity for company to leave a good impression on you as well as you to them, them being disorganized (often the case) doesn't really help much.