Here are two links to early Western writings on the history of the Langshan. Very different story. I wonder if the original imported stock was a regional variation?
“Every Courtyard Containing Large Black Fowls - M. Soulié de Morant tells me he was greatly surprised to find all the inner courtyards of the lower Monastery buildings where the apprentice monks and the servants of the Monastery lived, and in all the farms lying around the mountain and belonging to the Monastery, "beautiful, large, full bodied black fowls with a green metallic sheen", and these only. So unlike, he says the common fowl of the Kiang- Su Province, south of the Yang-Tse which were coarse and lanky, all of uniform colour, brown red, that of the wild fowls he had found in the Chinese forests.”
http://croadlangshan.org/pdf/THE%20LANGSHAN'S%20AMAZING%20HISTORY.pdf
https://books.google.com/books/about/The_Langshan_Fowl.html?id=ay9EAAAAYAAJ