As the title reads, the included offline DLC installer for Windows is a .sh file (linux shell script).
Just noticed this myself...would appreciate a return of the proper file for this offline installer.
Edit: So just out of curiosity, I tried swapping to the Linux offline installers and back to Windows again, and now I can download the Windows installer for the Community Level Pack DLC. It's a workaround, but odd that it defaults to the Linux installer in the first place for Windows downloads.
Edit 2: Same thing happens with the Anniversary DLC pack. Same workaround seems to apply.