@GrayBlackbird
They are a breed. A new one, and not recognized, but they should breed true. Not a first-generation cross-breed.
As I understand it (I could be mistaken) a slightly older new breed, called "Asian Black" was developed using birds of a Langshan type from somewhere in Asia. Not our western show and hobby type Langshans. Asian Blacks didn't impress anybody in the west, because they grow slowly and don't lay all that well compared to our production types. But people found them tastier.
In a lot of countries, fibromelanistic chicken meat commands a high price. People believe (probably correctly, according to the science) that it's got health benefits. So somebody took Asian Blacks and crossed them with silkies to get the fibro gene, and then bred the offspring back to Asian Blacks and selected the birds that were most like Asian Blacks except that they're fibromelanistic, bred those together, and kept selectng 'til they'd created a population where they're all herterozygous for fibro and are not silkie-feathered.