I found this on Motorola's website:
- Once the card has been formatted, you will be asked whether you want to migrate data currently on your device to the card. This step will move all media, pictures, and documents to the SD card.
- By selecting where to migrate content, you also select the preferred storage location for all applications, databases and data.
- If you decide to move that data to the card, the SD card will also become the preferred storage location for all applications content, data and database and media.
- If you decide to skip this step, your device internal storage will remain the preferred storage for all content.
So if you chose the SD card at that prompt, you should be all set. If not, one workaround would be to move everything off the SD card back to internal storage and then format the card — then repeat the process to make it adoptable storage, and select that option this time.
I should also add that Motorola's documentation seems to conflict with the official Google reference, so I'm not sure whether one is wrong or if Motorola has customized something.
Apps can be placed on adopted storage media only when the developer has indicated support through the android:installLocation attribute. New installs of supported apps are automatically placed on the storage device with the most free space, and users can move supported apps between storage devices in the Settings app.