This is not GDR3, we had the final build shortly after installing the dev preview.
From windowsphone.com, the OS version of official GDR3 is OS version: 8.0.10501.127 or 8.0.10512.142
This is something else. Most probably some minor bug fixes, certificate updates and general extra snappiness. May also contain some updates to support future hardware. It was pretty small in size, so I guess not a great deal to see.