There lies the thesis you pointed out. The point of these articles and coverage seems to be aimed at "Why isn't Japan multicultural yet, so racist!" which makes no sense. Japan has been inhabited by Japanese language, culture and homogeneous people for thousands of years.

There is absolutely no need for Japan to become multicultural or any other country for that matter because not being multicultural isn't a fault or a sin.

I don't know why so many in the West demand this on other countries. There's just something very unnatural and unrealistic and scary to expect a homogeneous country like Japan to suddenly start calling a clearly non-Japanese looking person Japanese. It's going to create huge problems for Japan that won't benefit it or its people by any measure.