It ain't very exciting, certainly nothing to soil your pants over.
No no no! You're missing it.
Create a blank text file, type "anything" in it, save it as anything.html, then open it and check the DOM again. You'll see that the DOM is there, even though you only typed "anything". Now, do a view source and you'll see "anything", but no head or body or html tags.
What's funky here is that view source shows nothing, but the document says, "Boo!" Which, is kind of spooky as the site hosts security material, and that's the home page.
For the OP, I was trying to point out just how backwards and out of touch the article was. It just took me by surprise seeing it, and then again, I thought about how very few people are aware of this -- present company excluded, of course.