The "Using Docker to cross-compile" tutorial claims the following:
Docker is a light-weight virtual machine with excellent cross-platform support.
From https://en.wikipedia.org/wiki/Docker_(software):
Docker is a set of platform as a service (PaaS) products that uses OS-level virtualization to deliver software in packages called containers. [...] All containers are run by a single operating system kernel and therefore use fewer resources than virtual machines.
This makes a comparison to virtual machines, therefore Docker itself is not a virtual machine.
The virtual machine used in the tutorial is QEMU:
Also, you will need to install qemu-user-static on your host computer, otherwise you will get an error: exec user process caused "exec format error".
qemu-user-static enables seamless execution of binaries compiled for architectures other than that of the host system. This is achieved using the binfmt-misc feature of the Linux kernel, which affects the entire system, including Docker containers. None of this is specific to Docker in any way; Docker is only used to isolate the build environment.
The "Using Docker to cross-compile" tutorial claims the following:
From https://en.wikipedia.org/wiki/Docker_(software):
This makes a comparison to virtual machines, therefore Docker itself is not a virtual machine.
The virtual machine used in the tutorial is QEMU:
qemu-user-staticenables seamless execution of binaries compiled for architectures other than that of the host system. This is achieved using thebinfmt-miscfeature of the Linux kernel, which affects the entire system, including Docker containers. None of this is specific to Docker in any way; Docker is only used to isolate the build environment.