It is quite normal to transfer the ferry fuel into the main tanks in order to get increased range.
But if the transfer pump system is not working as required it all turns very bad.
For any ferry tank system it needs to be double checked on the ground before the ferry departure date and again in the air before reaching the PNR.
This prang sounds like that but we will await the finding of the NTSB/FAA in xxx months time.
At least the aircraft wreck is to be recovered.
R