I agree that ultimately facts are what matter, but I disagree on this point. In the real world where it's not possible to author or reference a peer-reviewed research study for every statement or decision you'd like to make, this authority has value.
TThe administrators of Harvard Medical School, a well respected university, were willing to publish this content on a domain they controlled. This implies that some trusted expert at this trusted institution authored, reviewed, and published this content. This means that they don't believe that this content is so inaccurate as to expose the institution to a reputation loss, as opposed to say www.fake-health-expert.example.com. In fact, this may have more authority than a peer-reviewed study that doesn't properly disclose its funding by e.g. the dairy or sugar industry.
This skin in the game of reputational risk is orders of magnitude different than your or my reputational risk by posting a comment to HN.
No it does not. It is a blog post. Tons of people have blogs on that domain. There is absolutely no standard of authority or correctness involved. You are falsely inferring that there are trusted experts involved. There is no factual basis for that belief.