Inside of Linux, yes Docker does utilize cgroups, namespaces and some other stuff for isolation. However, the GP is almost certainly talking about "Docker for W

Inside of Linux, yes Docker does utilize cgroups, namespaces and some other stuff for isolation. However, the GP is almost certainly talking about "Docker for Windows" and "Docker for OS X", which do not run directly on the host OS, and need to be run inside of Linux VMs (like Vagrant).