Not an expert on ULD design, so a question. Do they have differential pressure protection. If you have a rapid decompression of the hold, (as part of the complete sealed pressure vessel), how quickly can they disperse their pressure, or could the ULD itself, experience an rapid decompression from a potential weak point, after the initial decompression? OK, it would be a minor event due to its volume, but could it be enough to detach part or all of its wall, allowing the baggage that is clearly seen, time to head toward the fuselage hole?
Or the baggage was just strapped down on a pallet!