The container runs a virtual machine using the host kernel's KVM device. Windows is then automatically installed inside said virtual machine.
Just for completeness sake, you can do native docker on windows on a windows host
Just no cross Kernel Linux on Windows (Unless passing over WSL) or Windows On Linux (Unless you virtualize in other ways and use that)
https://hub.docker.com/r/microsoft/windows#:~:text=How%20to%...
I'm kind of surprised you can "run Windows" in a Docker container at all. Isn't the fundamental restriction of Docker that all containers share the same (linux) kernel? Is there a way for docker to inject a "translation layer" somehow that makes it look like an NT kernel for the Windows processes?