No, apparently that's not tricky either - they simply let the users fill the knowledgebase using the unsuccessful guesses.
For example, if you think of a totally new character that the site doesn't 'know' yet, and hence it cannot guess correctly, you have a chance to tell them who it actually is. They store this info, so the next time someone else happens to think of this character, they'll have an answer sheet ready. Multiply this by the number of people using the site daily, and you've got a huge number of volunteers for smartening the bot up at a phenomenal speed.
Yep, Santa Claus doesn't exist, sorry.