Thanks for the comment, that was very insightful. I'm not sure I fully agree with this definition of plagiarism in academia though, but rather I am familiar with a broader one that includes both willful prearranged plagiarism and even self plagiarism.

In academia, the main discriminating factor to establish plagiarism would be the presence or absence of references, so in this case it would mean that the review would have had to include the ghostwriter as an author directly (and hence wouldn't be a ghostwriter anymore 😉