nah, it's not fixed. And if that example was fixed, CJ wouldn't just say "Oooh, i was in Prague 2 months ago!" Anyway, the question was probably not that easy so the average person who's been to prague would not know.
and what do you expect really...these guys have won so many quiz shows, first to win millionaire etc...if its 2 randomers vs 2 eggheads, and more often it is worse odds, the eggheads really should win.