Yeah exactly, it depends on what they do in the pipelines. If you just do a dotnet publish, it will not magically copy over everything that is in the git repository if it’s not part of the .NET project. Before most packages were converted to Razor Class libraries, I would have a manual step in the Azure pipeline that copied over all App_Plugin files.
If you have access to their Azure Devops and you can see the pipelines, you could check the generated artifact and see if there files are in there.