Yes, that maybe true, but they give you the option of opting out of your drone sending back data to DJI when you set it up. I checked that box.
Do they still send the data back? Who knows for sure, but if they want to use the data from my drone they’re not going to get much value.
If the drone cannot connect to a wireless network (unless it is an open network), it could not send data that way.
Maybe during a firmware update they could send data back? These use memory cards, correct? One thing would be to remove the memory card prior to a firmware update?