The article states that Microsoft has made a pull request to the existing repos to include the MIT license.

It was public already, what they are doing here is open sourcing the code.

Yes, but that happens to be the mainframe version. They are a bit different.

This is the source code to the original, non-commercial version of Zork that originated at MIT. Microsoft has now released the source code for the Infocom's commercial release for microcomputers.