Great find there! Is this a result of the recent cold weather do you think?
Just as an aside, by coincidence, yesterday I was reading some back issues of Porcupine! HKU's periodical and noted a record of Grey-sided Thrush in 1992 found at Kop Tong near Wu KAu Tang:
http://www.hku.hk/ecology/porcupine/acrodata/porc03.pdf
I guess this record was never accepted.