Yes this is an OTA update .. that's why i wrote "if i understand well" , because you didn't mention that..Although I didnt get any notification to update, the new firmware was from the 'Updater' app in the default system apps section. This is OTA update instead of external source I guess?
Unfortunately for me the official rom is something unknown , i just use it for 5 minutes to unlock it and put it in a drawer to pass 168 hours .. someone else maybe can help you..