Combining that and the pictures in the other thread referenced, I'd interpret that as the trip computer showing average MPG since trip reset (the stopwatch representing the latter).
It should be easy to check by changing the trip to display some other value (I'm not sure how that's done on the later models as the manual doesn't mention the button on the end of the RH stalk, and implies one might have to resort to the "Mode" button and underlying menus. There again, my manual doesn't mention the stalk button, but it is there and works).