How does "I have found my Internet Valentines 2010?" Facebook application work?

I have a friend and I'm quite sure we don't chat or communicate much compared to my other friends. I don't know what kind of algorithm they used, but without user input, she was included as my top one, I don't know how, but i think it got it right. And the second one also sounds true. There are top ten friends that it ranks, it basically almost got right the first five.