That's the first thing listed in the article? "Javascript to go fetch the HTML and insert it". What they're after is something that's _just_ HTML and not another language.
An embedded HTML page:
<object data="snippet.html" width="500" height="200"></object>
That said - it does appear encapsulated, much like an iframe - css doesn't take, etc. so though more "pure" HTML I'd argue doesn't fulfill the spirit of "include"?