There is some more info. One of his friends who was in a dinghy said that the bar jammed in the hook, causing a death loop, which he couldn't stop, probably caused by heavy gusts and an inconvenient fall. Maybe he didn't know that technique where you aggressively pull the further steering line to stall the kite and kill the loop, or simply it was too fast with those gusts to react. The autopsy shows he broke his back in 2 places, which paralyzed him and he drowned. He didn't hit any objects, he bounced of the water couple of times, which at those speeds was deadly. The guys on the dinghy got there as fast as they could, but unfortunately not fast enough.
As Toby said, precaution with the storms is crucial. But if you didn't manage to get out cause you didn't pay attention or smth (this spot is quite difficult, it's a river with a strong current, with forests on both sides, maybe it surprised him), and something fishy is happening (strong gusts, direction changes etc.) me personally, I always hold the hand on the safety, and am ready to let go of the leash as well. Also keeping the kite close to the water has it relatively less powered and you can last through heavy winds for some time. In any case, it's a tragedy and could have been unlucky mix of coincidences with no lack of caution from his side...really liked the guy, was listening to his rap at 10 showing off and all. RIP Gru.