Why is there more variation in Cambodian facial features than there is in Chinese facial features?

Question

I have had five foreign exchange students from Cambodia and they don't look anything alike. Yet we have three from China and they look pretty much the same.

Answer 1

Maybe you have myopia.

Answer 2

Cambodians are a mixed race with Chinese, Indian (from India!) and Malay elements. Both these last races are closer to our own, so our eye is more trained to see the differences.
Once you get used to Chinese faces, you will see the differences as well.