He's probably referring to "Windows Subsystem for Linux" which is a compatibility layer for Windows 10 that allows you to run unmodified Ubuntu binaries. It is also called "Ubuntu on Windows" since the userspace part is based on Ubuntu [2]

[1] https://en.wikipedia.org/wiki/Windows_Subsystem_for_Linux

[2] https://insights.ubuntu.com/2016/03/30/ubuntu-on-windows-the...