I think it's still open-source, it's just not free (as in freedom) software. I'm annoyed how suddenly redis, even when source is available, is put into the same bin as say MSSQL, with rest of the "proprietary software".
It's more like an especially generous version of shared source than open source.
[1] https://opensource.org/osd [2] https://www.debian.org/social_contract#guidelines
https://referencesource.microsoft.com/
You can mince words and make inconsequential adjustments to proprietary software licenses but they are still proprietary.
.Net Core and .Net Framework are separate implementations of .Net Standard.