It's a separate thin keyboard that's sitting on half the screen. There's another picture with the separate keyboard in the other Anantech article.
https://www.anandtech.com/show/15280/lenovos-thinkpad-x1-fol...
I can't quite tell... Can it be folded without removing the keyboard?
When folding it pretty much behaves like a normal notebook, where the screen folds onto the keyboard, only that there's more screen under the keyboard.