No, he meant that all the data that is currently on your phone will get wiped, after installing GrapheneOS it is like any other Android phone, but without Google. Here's a UnifiedPush alternative that uses Mozilla's push servers instead of Google's: 
It is something you'll need if you want push notifications (like incoming messages etc) from certain apps without killing your battery life, or at all.
Sunup | F-Droid - Free and Open Source Android App Repository
UnifiedPush provider using Mozilla's push server
