What is interesting about this picture is that the party portrayed looks like a cross between New Year's Eve (with the streamers and funny glasses) and Octoberfest (with the steins of beer). But Dong Zhi in Hong Kong is a very family-oriented holiday. Families try to have the meal together, and with grandparents and grandchildren there, there are no funny glasses or beer steins. The party in the picture is among friends and peers, not a family event. The characters say "Happy Dongzhi," but no one says that in Hong Kong.
Dong Zhi is celebrated as a special holiday in Hong Kong, and offices close early so that employees can go home and prepare large family meals. Though it is on the Chinese lunar calendar, it is not celebrated as a holiday elsewhere. It seems that as the holiday is being promoted in the mainland, it is being transformed from a family holiday to a peer-group holiday. Some anthropologists have been arguing that there has been increasing focus on the individual in the mainland, and this "holiday" seems to fit that pattern.