[mbrukman]

Blog post author here.

A virtual machine solution (such as VirtualBox) requires more CPU/RAM resources than a container, because you're running an extra copy of the entire operating system, in addition to your base system that you're always running.

A container is much more light-weight than a VM because it relies on the services of the underlying OS and just provides the runtime environment, but not the OS; please see https://www.backblaze.com/blog/vm-vs-containers/ for more detains on the distinction.

In any case, it would actually be more complex to use a VM, because I would first have to do a full installation of Ubuntu in the VM, before I could get started with installing the game, whereas with Docker, I can just build a container image starting with ubuntu:14.04 as a base, and have it working in seconds (minute or two once I started installing the required i386 packages, but that's unavoidable).

If you look at the end result, it's actually quite a simple Dockerfile, and the installation from start to playing will take you less time than installing a full Ubuntu distribution in a VM.