For example, whenever someone mentions "Korean girl", the Chinese male might conjure up in his head a Kpop princess with white skin, nice long legs and has a cute face.
Whenever someone mentions "Japanese girl", the Chinese male might picture some Japanese porn star who looks cute and innocent and screams like a little girl in bed.
Whenever someone mentions "Vietnamese girl", the Chinese male might think is that she is extremely sexy and horny in bed.
Of course these are really stupid examples that might not necessarily reflect the actuality of these other East Asian girls, but trust me on this. Whenever Chinese males mention or think about Korean girls, Japanese girls or Vietnamese girls, it is automatically assumed that they are attractive.
So even if the East Asian girl you are actually referring to is actually not that attractive, if you say "Korean" "Japanese" or "Vietnamese" followed by "girl", they will automatically light up and think that she is attractive unless proven otherwise. So it's kind of like the other East Asian girls all hot until proven ugly.
I have no idea what other East Asians' impressions about Chinese girls are like, but I'm not so sure that Chinese girls would be given the benefit of the doubt the same way Chinese males give the benefit of the doubt to all other East Asian girls.
If anyone who is reading this blog post now that is a Korean, Japanese or Vietnamese male, feel free to comment about your overall perceptions of Chinese girls. Thanks!