If I understand correctly, Facebook Connect uses OAuth and not OpenID. However, on Stackoverflow's login page, there's a short overview about OpenID, which gives an impression that all of the login options implement OpenID. Also, the javascript call to Facebook Connect is openid.signin('facebook'), which again gives the impression that FC implements OpenID. Am I missing something here?
OAuth and OpenID are not mutually exclusive. They do two very different things.
Facebook does, in fact, implement OpenID.