Some would find the very term "Asian" offensive. The reason we're "Asians" is because back in the day, they had to gather enough people for their voices to be heard.
As for identifying exact nationalities of those from some of the various southeast Asian countries, it can be difficult. Especially if it's just from sight alone. Cambodians, Loations, and some Vietnamese can all look alike. Usually their speech will give them away. There are Chinese that I, a person of Chinese descent, would assume to be Japanese or Korean if I was to just go by sight alone. Again, speech usually gives the nationality away.
Part of being able to identify each type of person is familiarity, and using clues other than visual ones, to identify who the other person is. If it was purely trying to identify nationality from a picture alone, I wouldn't know a Frenchman from an Englishman. And that's speaking as someone who has relatives in Europe. Of course other identifying clues such as accent would be needed.
Personally, I don't find any issues with what Wang Yi said, if it's looked at in purely political terms. He's trying to drum up support for an alliance, which China in the lead of course. My comment isn't meant to agree that China should be the one to lead. Merely that since Wang Yi is a diplomat or former diplomat, trying to increase diplomatic relations with other countries seem sort of part of the job. Again, this should not be taken as agreement that China should be the one to lead.