I think they're life rafts, but I think they're the sort of life rafts that inflate on contact with the water so just unused ones which inflated when it sank and they came in contact with sea.
The liferafts have water-pressure-activated automatic release mechanisms, plus lines that tie them to the mount with a weak link that will only break as the ship sinks completely. These liferaft mounts went underwater, so the rafts deployed on their own, but they're still tied to the ship.
