Confused...aspnet core 2.2 containers on linux or windows

Hi,

I have noticed a number of aspnet core 2.2 docker images that are built from microsoft or docker aspnet core images (which are clearly not linux) but then it runs linux commands to install other items like node or something else using apt-get, etc as shown below.

FROM microsoft/dotnet:2.2-aspnetcore-runtime-stretch-slim AS base

RUN curl -sL https://deb.nodesource.com/setup_10.x | bash -
RUN apt-get install -y nodejs

others use similar aspnet core 2.2 base images but use powershell for installing nodejs.

Im confused. It would seem like any of the aspnet core 2.2 images would NOT have apt-get.

does using apt-get or powershell just depend on the host OS that is being used to build the docker image? In the above docker file set of commands, apt-get clearly doesnt exist on the base image microsoft/dotnet:2.2-aspnetcore-runtime-stretch-slim.

can somebody help me clear this up? is there any documentation that would help clear this up?

thanks