Picking between the usual dross there have been some interesting points made and I have learned a few things from the discussion of this incident.
The first thing is that there are amazing differences in attitude towards auto landing. They seem to range from don't do it unless it is absolutely necessary to it being no big deal.
Whatever various parties would like us to believe autolands in better than low visibility conditions occur frequently. This seems to be the only serious incident. At least nobody has cross referenced to anything similar. Why might this be?
In this case a fail operational aircraft veered off the runway while in rollout mode. As Clandestino agrees an aircraft overflying the localiser antenna could have caused the interference. This appears to have occurred at the precise moment the 777 was transitioning into rollout mode. In this mode the automatic go around function is disabled, which is not something that seems to have been the focus of training (in Singapore airlines at least).
So the holes in the swiss cheese line up. Had the runway been shorter the interference would have occurred at a height where the pilot would in all likelihood have avoided this happening. Had the aircraft been fail passive the autopilot would have dropped out rather than heading for the grass. Had the crew been trained for this eventuality they might have responded more appropriately. All supposition of course, but it has made me think a bit.