I don't think it's necessarily a "white people" thing, but more just the people you're familiar with. Twenty years ago, I for sure wouldn't have had the slightest idea of how to tell the difference between a Japanese, Korean, Chinese, Filipino, Thai, Vietnamese, etc. These days I can identify their nationality with a fairly high degree of accuracy simply because I've been exposed to so many and now know what their characteristics are.
It's the same with some people from places where they haven't seen a lot of white people. Lots of white people look the same to them. In Korea it's still quite common for Korean children to call any white foreigner "Miguk Saram" which means "American". In the Philippines, white foreigners are often called, "Joe", I guess due to their exposure to American servicemen nicknamed "G.I. Joe". In Thailand, the English are probably the most common tourists, and as a result some Thais presume a foreigner is from England. I've seen numerous Thai websites that have icons for a Thai flag and U.K. flag for indicating "Thai Language" and "English". A good number of Americans likely would have no idea that the Union Jack signifies English.
In Asia I've been mistaken for being English, German, Russian, Canadian, and Australian. One guy in particular always asks me, "how's Canada" and such things despite having told him a dozen times I'm not Canadian. Asians are often confusing me with other foreigners they know. I've lost track of how many times people have said I look just like the "KFC grandpa", despite not having a mustache, goatee, nor white hair like Colonel Sanders. I just don't let that kind of thing bother me.
