runtime: Environment.OSVersion.Platform returns Unix on macOS

Using .NET Core 2.0 SDK preview.

dotnet --info:

.NET Command Line Tools (2.0.0-preview1-005977)

Product Information:
 Version:            2.0.0-preview1-005977
 Commit SHA-1 hash:  414cab8a0b

Runtime Environment:
 OS Name:     Mac OS X
 OS Version:  10.12
 OS Platform: Darwin
 RID:         osx.10.12-x64
 Base Path:   /usr/local/share/dotnet/sdk/2.0.0-preview1-005977/

Microsoft .NET Core Shared Framework Host

  Version  : 2.0.0-preview1-002111-00
  Build    : 1ff021936263d492539399688f46fd3827169983

Simple test case:

[12:41pm yaakov@Eadu:/tmp/osver] dotnet new console
The template "Console Application" was created successfully.

Processing post-creation actions...
Running 'dotnet restore' on /private/tmp/osver/osver.csproj...
Restore succeeded.

[12:41pm yaakov@Eadu:/tmp/osver] vim Program.cs 
[12:42pm yaakov@Eadu:/tmp/osver] cat Program.cs 
using System;

namespace osver
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine(Environment.OSVersion.Platform);
        }
    }
}
[12:42pm yaakov@Eadu:/tmp/osver] dotnet restore && dotnet build && dotnet run
  Restoring packages for /private/tmp/osver/osver.csproj...
  Lock file has not changed. Skipping lock file write. Path: /private/tmp/osver/obj/project.assets.json
  Restore completed in 177.16 ms for /private/tmp/osver/osver.csproj.
  
  NuGet Config files used:
      /Users/yaakov/.nuget/NuGet/NuGet.Config
  
  Feeds used:
      https://api.nuget.org/v3/index.json
      /Users/yaakov/.dotnet/NuGetFallbackFolder
Microsoft (R) Build Engine version 15.3.117.23532
Copyright (C) Microsoft Corporation. All rights reserved.

  osver -> /private/tmp/osver/bin/Debug/netcoreapp2.0/osver.dll

Build succeeded.
    0 Warning(s)
    0 Error(s)

Time Elapsed 00:00:02.29
Unix
[12:42pm yaakov@Eadu:/tmp/osver] 

I would expect the program to print MacOSX, i.e. System.PlatformID.MacOSX which is enum value 6.