A flash could have blinded him for a few seconds, delaying his recognition of a developing situation. Perhaps if he had noticed a few seconds earlier, he would have had enough time to correct the problem.
In any case, we won’t know until the investigation report is released.
That “developing situation” started in Seoul, Korea when the pilots were planning the flight. In my opinion, the error chain began there with a poorly matched check pilot (trainer) and a weak Captain and crew. Most likely, the crew missed the fact that the ILS approach facilities were out of service for 28L and 28R. Knowing this, they would have had a flight across the entire Pacific Ocean to plan a non precision approach using the excellent Flight Management Computer to build an approach with alignment and glide path information that could have been autopilot coupled and flown to 300 or 400 feet. “Flash of Light”? I sincerely doubt it.