In fact, the two different directions actually indicate different things. Anti-clockwise is 'request sent, waiting for any kind of response' and clockwise is 'request received by server, sending response' (and the browser is downloading it/processing it, extended periods may mean it is doing all kinds of third-party lookups and stuff)
The brief anti-clockwise here is no different, there's some additional request being triggered after the main page has loaded. Facebook resources for example, though there can be others.