There were several questions that Shaun got wrong that you'd expect him to get but I suspect nerves played a huge part in it. I am sure that, in the comfort of his own home, he would have answered several of those questions correctly.
Having entered AYAE I can assure you that answering questions in your living room and answering them in a TV studio (with all the lights and cameras on you and all the production staff racing around all over the place) are two entirely different propositions. I know that on several occassions I was so scared I could barely think at all, never mind try to think of an answer. It is much, much harder than you might imagine. Which, as far as I can see, makes Barry's performance in the final all the more remarkable.