I have no idea,
Was realy confident through all my training and test etc, its only when im sat in a room with 2 people looking at my licences I seemed to have a mental block at one point. He asked me " so how do our jet engines work?" It took me by surprise and I had to think about it, its one of the simplest bleeding questions we could hope to be asked!!
It may be the fact that most of my day was spent waiting in suspence, I was the last one there and didnt get intot the interview untill 4:30 having arrived at around 8:20. Not good to sit and stew!
Like you I must have done something right.
Nick