How to Tell Chinese, Japanese, and Korean People Apart

I was wondering how to distinguish people from various Asian nations.  I did a search and got some very intelligent explanations as well as links to sample photographs.  But I wanted to rephrase and pass on an explanation that seemed very practical.  I don't actually know whether it's true.  The Asian woman who posted it says she got it from another blog, but I wasn't able to find that other source.  So my rephrasing of her theory goes like this:

Suppose you're at the airport.  There are three groups of ten Asian people.  In the first group of ten, one person is talking.  Everyone else is smiling, listening, and occasionally responding to the speaker's questions or remarks.  These are the Japanese.  The unity of the group is their priority.

In the second group of ten, everyone is talking loudly at the same time.  These are the Koreans.

So now we know the third group must be the Chinese.  In this group, half of the people are talking; the other half are looking around, seemingly at random.  I'm tempted to add:  "This is because the group is simultaneously gathering and processing valuable information."  But I think the better reason is, as someone pointed out in one of these websites, China is a big and diverse place, with a good assortment of cultures.