USMCProbe
The "frayed and broken earthing wire" looks like it was mechanically destroyed. I.e. somebody wanted to take the battery out in a hurry and didn't have the right tools. It is not burned/welded/melted. Somebody took a pair of pliers to it. The firemen did it.
I haven't seen any good pictures or scans of the ANA battery. I thought it was burned so bad that they couldn't really make a valid conclusion. The JAL battery was "lucky", in that they stopped the fire before complete destruction and they got a good look at the failure mode.
out of this reference from today
Japantoday
Photos distributed by the Japanese investigators show severe charring of six of the eight cells in the ANA 787’s battery and a frayed and broken earthing wire — meant to minimize the risk of electric shock.
There are some photos as well in the above reference.