Not a range extension
Sorry if this seems like a very pedantic point, but a single record does not constitute a range extension. We have one record of Steppe Eagle in Hong Kong, but that does not mean that SE China is part of the range of the species. A range extension constitutes more or less regular breeding, migration or wintering occurrence.
There is an underlying point to this comment - if we in China talk about the range of Great Thick-knee as extending to Hong Kong, then the BirdLife International database may start to treat SE China as part of the range. That could have the consequence of downgrading threat status (which is partly based on the area of the range); and it would all be on the basis of a single, almost certainly, lost, vagrant bird.
In the words of the BBC in UK during WWII: 'Careless talk costs lives'.
Mike Leven