This is kind of touching on some of the stuff that came up in the Discuss racism thread recently - why would we limit "Asian" to a certain collection of countries and not others?
Possibly precisely because Asia is so large, and the people born and living in Asia are so enormously diverse, that "Asian" meaning "a person from the Asian continent" is not a useful classifier. You could probably find someone in the 60% of the human race that lives in Asia who could easily be confused with a native of any other inhabited continent.
The division of continents is arbitrary and doesn't account for overlapping areas like the Middle East or Central Asia. An Egyptian or Algerian would be "African" in terms of geography, whereas an Iraqi or Saudi Arabian would be "Asian", a division that makes no sense culturally. Someone from Lebanon would have far more in common with an "African" Egyptian that with a "fellow Asian" Japanese person, and I think this is why nobody actually ever calls Lebanese people "Asian".
In people's minds, I think
ethnic appearance trumps geography every time. In Australia, and I'm sure in the UK or USA too, it doesn't matter how many generations your racial-minority family has been living in the country, if you look different from the majority, your ethnic appearance will dominate people's perception and identification of you. I was born in China, but many of my "Asian" fellow-citizens were born in Australia, and it is our common ethnic appearance, not our diverse places of birth, that dominates people's perception of us as "Asian". By contrast, if he were not wearing the uniform of a general in the PLA, how many people would pick out
Lin Hu as "Asian"?
The "
one drop rule" seems still to be alive and well too, judging from the way in which Dichen Lachman is so often referred to on the internet simply as "Asian" rather than "Australian". A few years ago, I was shocked to read a forum posting questioning whether
Joanne Missingham should be representing Australia in the 2008 World Mind Sports Games because she was "obviously Oriental"...