It's a good recent count but it's nowhere near the highest, which is 30 at Tai Po Kau on 23 November 1969 (see Avifauna page 417).
This species was more common in winter at Tai Po Kau before 1980, particularly in the late 60's and early 70's. In those days it was mostly a winter visitor to Hong Kong.
Since then it has become mostly a late autumn and spring passage migrant with only a few in winter - see this chart which shows occurrence by week over the year for the following periods - 1959-1979, 1980-1998 and 1999-2013
