Oops! The factor of safety is defined as, “The ratio between the breaking load on a member, appliance, or hoisting rope and the safe permissible load on it.”
The safety factor is the ratio of designed breaking strength to the maximum expected load. Generally, the load is limited to the working load, which is generally less than the maximum expected load. The working load is called the safe load.
" It's hard to see how a multi-thread wire cable would snap."
They do snap. Generally wear, fatigue and strain in the outer fibers result in a higher stress on the inside fibers. If the cable isn't lubed right, or is subjected to a kink, or small radius bend, they tend to snap. When cables and ropes break under stress, they are like bull whips. All the energy that was in the cable before the break ends up as motion of the cables. Since the riders saw the broken cable before it dropped, it looks like it broke at, or near an attachment point where it was crimped, or subjected to fiber movement and subsequent damage from friction. Crimps tend to strain outer fibers and increase the frictional force between fibers adjacent to the crimp.
Sad something like this would happen. I think it was easily preventable.