Ultimately it is still in the interest of Microsoft if their toolchain is interesting because it is compatible among all target devices (PC, Xbox, PS, Mobile) so I'm unsurprised they are moving in that direction.
Under Balmer's time, there already publicly existed Microsoft Rotor - a .net runtime that ran under FreeBSD and OS X:
> https://en.wikipedia.org/w/index.php?title=Shared_Source_Com...
So don't do a corruption of historical facts.
The impression I got back then was not so much of Microsoft showing how "cross-platform" .Net was, more like a big middle finger towards Linux.
It was a unsupported (no release after 2006) bare fork of the runtime that couldn't be used commercially [2]. Would you have corrected me if I stated "Internet Explorer doesn't run on Mac Os X" just because there is a version of it from 2003?
Especially when you compare it to a large part of the toolchain including compiler and runtime under a MIT license that builds to multiple platforms from the same codebase [1], that's not even in the same league.
[1]: https://github.com/dotnet/
[2]: From your own "This license [...] allows for personal or academic usages, but they can't be used for commercial products"
Without kidding: I actually know Apple fanatics who use this to "point out" that Internet Explorer does run on OS X and use the argument that this version is from 2003 to show how badly Microsoft treats Apple users. :-)