> My biggest problem with the word is that it is used sloppily. It conflates race, culture, language and nationality and assumes a kind of all or nothing approach to them

Westerners are no better - the US does the same for everyone who is not "default" (i.e. white) where they are differentiated by a prefix, usually their heritage, which conflates "culture, language and nationality". Your black Japanese student would be considered "African American", which is beyond absurd.