What determines which people come up at the top of facebook chat?

On facebook, there's always about 10 people both offline and online that appear at the top of faceook chat. People move up and down all the time so it changes a lot except about 4 people I talk to lots stay there all the time. However, there's this guy I like and I admit I look at his facebook page quite a lot and I've never talked to him on facebook or liked anything or commented but he appears at the top every time he's online. What does this mean? I look at other people's pages a lot more than his and chat to people and like their stuff but they never appear at the top of the list at all... Help?