At that altitude with the camera pointed down at the water, all you can see is water. You can't tell whether the drone is descending or the water is rising up. Looking at the controller screen, you could only see that the surface of the water was...
Not the first time he's had this sort of problem.
"I was flying a series of out of signal range waypoint missions over train track and terminals under construction near my house."
Crash.
"... the drone was way off course, and ended up hitting...
If you're talking about the empty car window breaking in the video, that wasn't a threat, it was a demonstration of the nation's new defensive capability.
Why would DJI void the warranty in Japan just because you took the drone to another country.
Just ask them how they're handling such cases. Worst case, you won't care for the answer, but they've not going to be vindictive because you asked.