The point of open source is to address and concerns around copyright. And this source is not open source by the definition most people use when they refer to “open source”. It’s still proprietary but source available.
However I will say, this source is unlikely to be useful to anyone beyond academic curiosity. So for the purposes of this project, the source license is “good enough”.
We should care about Microsoft's licenses exactly as much as Microsoft cares about ours.
More concretely, Microsoft's license [0] gives you at most one of the four essential freedoms:
0. Freedom to run for any purpose? No.
1. Freedom to modify the program? Maybe; Microsoft can revoke it without cause at any time.
2. Freedom to distribute unmodified? No.
3. Freedom to distribute modified? No.
I'm using the free software definition [1] because it's simpler and clearer than the open source definition [2], which is usually considered mostly equivalent in practice, but as far as I can tell Microsoft's license satisfies zero of the latter's ten criteria, apart from perhaps non-discrimination and technology-neutrality. Most of the criteria of the open source definition have to do with distribution, which is not allowed by Microsoft's license.
[0] https://computerhistory.org/blogs/microsoft-research-license...
[1] https://www.gnu.org/philosophy/free-sw.en.html
[2] https://opensource.org/osd