Try thinking reverse psychology.
You decided you were probably going to fail so a word popped in your mind that wasn't in the dictionary. Then a second attempt because the first one made you think you failed and another word not in the dictionary.
Perfect score
you wanted to prove to yourself that you probably can't do it and so you picked two words that were not possible to find in the book.
A bit of a paradox because to make sure you couldn't do it it had to use words that weren't there... how did your mind know it that those words would be impossible for you to find?
Think about it.. It's a sneaky trick your mind is trying to play;)
Don't worry too much about the dictionary game. It's a game. Just continue with the rest of the course.
Alex