Software update is sent out to Motorola Moto Z users to fix low notification volume issue and more
Considering that the size of the update weighs in at 540MB, you would have to expect that more than just one bug fix was included. To be sure, the phone shows that the last security update was installed in November, and Android 7.0 is still running the show.
Keep in mind that this update is for the unlocked version of the Moto Z, not the Verizon exclusive Moto Z Droid sold in the U.S. And because it is being sent OTA, the update is being disseminated in waves. That means it could take a few days before it arrives. You can try to manually download the update by going to Settings > System updates > Check for system update.
Once you receive notification that the update has arrived, make sure that you are connected to a Wi-Fi signal before starting the updating process. Also, be sure to have your battery charged fully before you install the new files.