All of your assumptions makes my head hurt. To know what actually happened, you'd need to know numerous variables that can't be seen just by looking at the video. It really doesn't matter what you believe what what happened based on the video because you're not seeing close to the full picture.
Just a few things to consider...
1. History of incidents for this and other of the same type of ships. This isn't a new problem.
2. Who was actually piloting the ship.
3. Was this mechanical malfunction or pilot error or something else?
4. How did the ship lose power? The lights going off and on doesn't necessarily tell us when the engines shut off or if they regained power.
5. What were the conditions of the currents. Currents are strong enough to move ships, especially when they aren't tied down. Anchors are pretty useless in stopping a ship with no power and caught in a strong current.
6. It typically takes months and years to investigate incidents like this. To think we can know what happened from a video and incomplete data just hours and days after is absurd.
7. There's certainly more I'm probably not thinking of at the moment. But until proven otherwise, the simplest explanation is a maritime accident. This has happened before, and likely will happen again.