I suspect the author was being exact and referring to the product just called 'MacBook', rather than referring vaguely to a MacBook Air. (I can't back that up,

I suspect the author was being exact and referring to the product just called 'MacBook', rather than referring vaguely to a MacBook Air. (I can't back that up, except to note that Apple fans are usually fairly scrupulous about referring to their MacBook Pro, iPad Air, iPhone 6S etc specifically rather than lumping them together). In any case the current MacBook is quite similar to the MacBook Air and the rest of your comment probably stands.