The flash was reported by the people present, but there was no camera to verify it. Could it have been optical illusion from other radiation?
I think he was the only one to get a lethal dose because he was standing right over it. The others were not standing as close.
Distance is pretty effective in a lot of cases, as increasing distance reduces dose due to the inverse square law.
Getting 100 units of exposure at 1 foot away drops to 25 units at 2 feet away. Going to 4 feet drops it to 6.25 units.
At the levels of radiation I dealt with, simply using tongs was enough (behind a body shield, of course!) Your hands can take a lot more than your body.