Not familiar with Arthur Machen, but on clicking that link i realised i actually had read that story years ago, when i was perseverating on cryptozoology...
Reminded me a lot of HP Lovecraft. IMO both Tolkien and Lovecraft were probably aspies, and a lot of Lovecraft's characters also are (Charles Dexter Ward is one of the best examples)...
When roughly was Machen writing? His style suggests to me that he was probably writing a few decades before Tolkien, possibly around the same time as Lovecraft...