As I have said earlier on this thread, I spent 16 years of my life fishing for crab and lobster, picking up buoys of this size, in tide like this. On average we would pull 600 pots a day, and our season would last year-round. I have seen this scenario, as videoed, maybe over 100,000 times. That buoy is acting EXACTLY how it should be acting if it was anchored to the seabed in some tide. You may want to see some wake at the front and sides, but it doesn't happen like that. Indeed, on some tidal cycles when the current pulls so strongly that a buoy is underwater, the wake will appear several yards behind it.
Let me explain better what is happening in the video - imagine a clock-face where the tide is running from 9.00 to 3.00, with the buoy anchored in the centre. The yacht is travelling from 4.30 to 10.30. as it heads across the clock-face, the current running from left to right will push it down onto the buoy. As the boat closes with the buoy, the crew assume the buoy is moving, but it is not - the boat is. As the boat passes the buoy the buoy itself seems to "move" round the stern. At this stage the woman at the helm goes hard to starboard, you can see the wake clearly moving to one side - at this stage the buoy seems to accelerate but in reality the boat is now going 6.00 to 12.00, and is now going down-tide, away from the buoy.
I would assume, from the crackily radio reception, that the interview in the video takes place well away from Sweden - but still somewhere in European waters because of the way the crew are dressed. In some ways this would make sense since (1) there is little tidal movement in coastal Swedish waters and so the crew may have been very unaccustomed to seeing this scenario, and (2) almost anywhere south of Denmark the chances of encountering tidal currents increase.
There is no USO, no sub and no fish involved in this video. It is almost certainly a white buoy, as used by a pleasure-boat, which is marking an anchor on the sea-bed which the pleasure-boat crew have been unable to raise due to the tide. At slack water, I bet they returned and pulled both the buoy and anchor up.
I trust this guy's opinion because his avatar is a fish. Fish avatar says not a USO = case closed imo.