I think he means the newer versions of the stack, from the release of .NET Core 1 in 2016 and onward.
More then 50% of the VM's in Azure run Linux and not Windows. On AWS and GCP the percentage VM's running non-Windows OS'es is probably even higher. That's a realistic threat to the continued existence of .NET if .NET only runs on Windows.
Who doesn't like to talk about it? It's so much easier to integrate components on Linux over windows. Why would anyone willingly use windows for data analysis?
I don't think that's bias.
It's really nice not having advertisements in my start menu.