He's providing some background information for the "Beyond the Threshold" game entry.
Of course, being a huge fanboy of the Cthulhu Mythos, I feel it my obligation to add even more information where it is needed.
Von Junst and his book "Unspeakable Cults" first appeared in Robert E. Howard's story "The Black Stone." The story can be read here
http://www.feedbooks.com/book/1666
Although the story's focus is centered around the nameless narrator's search to find a large and ancient black stone in Hungary and the horrible discoveries he learns when he dares to delve into its origins, the strange death of Von Junst after he finishes writing "Unaussprechlichen Kulten" is the premise of the game "Beyond the Threshold."
The game attempts to provide a more detailed account of how Von Junst died and what he did just before his death. There are no virtually no details as to the cause of his death in "The Black Stone."
As the internet folk say, Junst got P0WNED by the Great Old Ones