if you look at the first picture you cant see the trailer wheels at all, and the front of the boat is far out on that trailer which means the front end of the trailer is really heavy, has not been balanced properly by look of it.
the stock navara tow ball only has a rating of like a few 100kg of TOWBALL weight, compared to the 3T of actual TOWING weight. sure it can pull the boat fine, but with all cars you can only put a certain amount of weight on the towball itself.
eg. dads got a 3.5T trailer full of tools n stuff and hes never had a problem with his car, but thats because the trailer is fairly balanced. its on dual axle with more weight towards the back, so basically it just free stands without the front end falling to the ground.