What you are referring to is "The Endor Holocaust".
In universe, it was "a theory put forward by Imperial propaganda agents after the Battle of Endor." In fact, Endor was saved :
Much of the debris of the superweapon was sent through a hyperspace wormhole that briefly opened up when the Death Star's hyperdrive regulator was destroyed.
According to the man's fellow cantina patrons, most of the Death Star's mass was obliterated in the explosion, while the Rebel Alliance used tractor beams to ensure the rest did not damage the world. [...]
At least one Imperial Star Destroyer did crash onto the moon's surface, though, and some debris was reported to have caused minor damage to Ewok habitats.
Out of universe, the link you submitted is "Original content is © copyright Dr Curtis Saxton 2002." (scroll to the bottom to see this mention) There's a mention of this work in the behind the scenes section of the Wookieepedia article.
The Endor Holocaust theory was first put forward by Curtis Saxton on his Star Wars Technical Commentaries fansite. Saxton claims that it is scientifically inevitable for the holocaust to happen, though it has never been identified as happening in any canon source. Some sources, such as X-wing: Wedge's Gamble and the comic book Apocalypse Endor, mention the theory, though reports in these sources are either propaganda or myth.