It’s not uncommon for the App Store/Software Update to make no distinction between the final GM seed and the production version, making it say you’re already up to date if you’re running the GM seed. They’re usually close enough to production that the GM seeds can update to x.x.1 type updates.

That said I’m downloading the official release now and installing it over my GM seed install simply to get beta releases of 10.11.1 to stop showing up in my updates tab.