This video quite graphically shows the massive boulders and rocks that have fallen. It's quite ironic that the first sign you see as you approach Steall Gorge warns of falling rocks. Thankfully no one was on either of the paths covered by the fall.
The video makes for quite a sobering reminder of how small and vulnerable our species is when confronted by "Nature" at its worst, particularly the final shot showing just how high the landslip started. As you say, it's a relief no-one was in the boulders' path when they came down.