The point is that the ac commander has a responsibility to manage the risks of any landing site
We know helicopters have landed on this yacht before . The helideck would have been certified up to a certain weight by the builders and registration authority. Part of the Ships Orders would be the instructions to make the deck safe for operations.
The pilot would, as I have done on innumerable operations all over the world on everything from 1,000 to 350,000 gross tonnage, land on the deck knowing that it is fit for purpose with absolute confidence.
There is nothing the operator can do beforehand and in this case there was nothing the pilot could do when it happened.