I guess it's possible that they're doing the same thing as recaptcha - for some questions they already know the answer, others they're going to use your answer as a data point.
See my reply to another comment - the data doesn't exist. In some images I was supposed to identify random objects or blanks walls as my friends. So they do use this to train their algorithm and/or complete their database.
They get you to put names on faces in pictures.
Only sounds like identifying already tagged images from the article, no extra information they don't already have.
How can they use that for authentication if they don't already have the data to see if your answer is right?
That's why I'm thinking that they don't use it for authentication. There were quite a few steps to go through, so my assumption would be that some steps are used for authentication and others are used to collect data.
Man, I'm realizing I must sound paranoid about Facebook.