It seems to me that it's stating facts about the essays, not necessarily making or quoting a broader statistical statement. It's like a reviewer writing that "

It seems to me that it's stating facts about the essays, not necessarily making or quoting a broader statistical statement. It's like a reviewer writing that "Hunter Thomson writes about his time in Las Vegas which is largely drink and drug fueled" and you asking for statistical proof that Las Vegas dynamos run on beer and cocaine. The review is talking about the subjects of the specific works being reviewed, not necessarily the world at large. That's why I quoted more context from the review, to make that clearer.