Do I get this right?

- they concentrate salt water once to get "heavier than sea water" brine. Hope not chlorinated.

- it's then a closed system shuffling between bottom and top tank(s)

- everything floating is soft, so no strong forces unless a wave crashes on top

- advantage of ocean: "free standing" within height/depth margins, free water for initial fill

And really not visible in the video:

- the disk you see floating is a V shaped bladder with the storage in the V below surface and floatation sprinkled all around and segmented in to "cake wedges".