Every single example I can find makes it painfully clear it is an undirected graph. Sets may differ going from one direction to the other simply because it is only trying to find a sample set of correlations, not an exhaustive set.
The graph is most definitely directed. One small example is Facebook -> Narcissism (1 path of 1 degree)[1] compared to Narcissism -> Facebook (8 paths of 2 degrees)[2].
Philosophy links to neither sexism or "The Demographics of Africa" (and while some older version might link to sexism, it seems unlikely that it ever linked to the Demographics of Africa"). Both of those do link to Philosophy, however.
Alternately it is directed, except when it doesn't find an easy route and uses an undirected result.