sn_master is talking about a "self-contained, single file deployment" that does not need an existing shared runtime present on that target machine (or container). This is an orthogonal concern to running on Linux, which could depend on a shared runtime, or not.

Self-contained deployments are platform-specific.

A deployment that depends on a shared runtime can be cross-platform, since all the platform-specific parts are in that shared runtime installed for that machine's platform.

Which does .NET do? all of the above.

https://learn.microsoft.com/en-us/dotnet/core/deploying/