See: pkg/build/node/node.go, this image is built programmatically with docker run / exec / commit for performance reasons with large artifacts.

Roughly this image is the base image, with the addition of:

• installing the Kubernetes packages / binaries
• placing the Kubernetes docker images in /kind/images/*.tar
• placing a file in /kind/version containing the Kubernetes semver

See node-image for more design details.