I think those are just two runners (the Moroccan Windowpane Rug) from West Elm going down either side of the island. i have a big one in my living room that I bought a few years ago. i think it's just the way they're placed that make it look carpeted.

Also, I don't think it came in black- mine's the espresso color which leads me to believe that maybe that kitchen photographed darker than it really is. Maybe the wood is all a very dark espresso stain and not black?

Regardless, you're right, it's a great example of a limited palette pulling a room together! I love those tall cabinets!