I'm not entirely sure what happened there. It almost looks like the descending guys twisted the ladder, or tried to 'walk' it while they were on it.
Ladders, btw, are rated for full load on every side that has steps. That is, a 250# rated mechanics ladder (arranged like the one in the video) is rated for 250# on both sides at once.
Looking at the ladder as it lay on the floor, it looks to be in perfect condition. That is, no remaining twists or kinks in it. I don't think the ladder 'failed.' I think this was an 'operator' failure.