The definitions are from the Cold War: industrialized capitalist nations in the West, communist nations in the East, and none of the above, where the proxy wars were fought. So the definition is fixed by history, and also somewhat obsolete.

Note the amusing parallel between assuming the US is turning into a "third world" country, since the gaps in industrialization worldwide are closing, and the article's original assumption that an educated middle-class girl would never have to do the same work as a Spanish-speaking working-class woman.