The problem is all they're measuring is the genetics of this locality, or any locality. You acquire your friends mostly through geographical proximity; in most places, the people nearest you are going to have a certain level of relatedness.
But this has less to do with friendship and more to do with geography; they might have achieved a similar result by comparing people to their neighbors.
But this has less to do with friendship and more to do with geography; they might have achieved a similar result by comparing people to their neighbors.