I found the article confusing and somewhat pompous, especially when in the last paragraph he conflates ‘multiculturalism’ with having a multiplicity of ethnicities – they are entirely different things. Smith is one of the worst offenders among western observers of Japan who insist on trying to frame every Japanese problem as if Japan was America.
The first time I travelled to Japan I was struck by how varied the faces I’d see on streets in Japan were compared to China or Vietnam, which are both far more homogenous, at least in terms of how people appear. The Japanese are ethnically quite clearly a mix of East Asian, Polynesian and Siberian. The Ainu are of course one strong element (they were pretty much self governing in Hokkaido up to the late 19th Century), and yes, they’ve been strongly discriminated in the past, as have ethnic Koreans, ethnic Okinawans and the Burakumin, who are essentially a ‘lower caste’, but who many Japanese consider a distinct ethnicity (they are probably the descendants of meat workers and roving workers, a little like Irish gypsies).