Hi petra,
I noticed that earthquake too. Also it was followed a little less than two hours later by a small earthquake on the Hayward fault near San Leandro. Another interesting earthquake on the Bay Area map was a 2.1 7km S of Antioch on 01-06. It was within a 9 kilometer radius of the 5.9 that occurred in January 1980.
Thought these three recent quakes might be somehow tied into a pretty sizeable change in strain that is showing on the Ohlone site of the SF Bay Mini PBO.(although the quake you mention should also be covered by the St Vincent's site of the Mini PBO, which hasn't shown much strain change for a few weeks)