Note: This tweet thread was written when only the 15th-17th centry segment was posted. I have gone back and added elements about the other segments subsequently added, up to the 1920s article.
Victor Krum. Brain, you are SO very fired.
(Note: I totally made that term up, but if you watch Dr. Who long enough, you will start to notice that every episode takes this approach to teaching kids something or other)
This is reinforced and made clearer by later posts in the series; for example, the 1920s post states:
"After the Great Sasquatch Rebellion of 1892 (for full details, see Ortiz O’Flaherty’s highly-acclaimed book Big Foot’s Last Stand)"
Big Foot's Last Stand is obviously not a book that exists (and would obviously be really problematic if it DID), but the article references it as if it does, demonstrating that it IS written from the perspective of a fictional, UK-based magician educating young, UK wizards, and drawing from horrifically Euro-centric texts, rather than being written from the perspective of Rowling describing her fictional world to us.
It has been pointed out that these essays are being released in a period of time when Fantastic Beasts and Where to Find Them film adaptation is being promoted. That film is based on the book, which was written as a text from the late 1920s. So it is likely that the Pottermore posts are not only from the perspective of a white wizard, but a white wizard from a time period when white people were even more deeply stupid about this stuff.