The fluting is clearly rotational wear. The theory posted above is that the rotational wear at that level is due to micro pitting that is caused when electricity arcs between the balls and the race. The arcing will happen because there's not a great mechanical bond between a ball and a race, kind like a loose electrical wire can cause heat buildup and arcing. The micro pitting will occur whether the bearing is rotating or not. Once there is a pit in either the ball or the race rotation will cause the pit to transfer defects to other balls and other parts of the race.
I can easily cause pitting around a poor welding ground clamp. I can also weld with a car battery, jumper cables and standard stick welding rod, so it's not like we're out of the realm of possibility on a car from either the battery or from the alternator. 12v dc at 90+amps is sufficient to throw a very strong electrical arc and vaporize metal.
So, I'll stand by my statement of plausible.