Tell him to wear his seatbelt, just like the Flight crew told him half a dozen times between when he boarded and when this happened.
People who are belted, get surprised by clear air turbulence.
People who are too stupid to wear their seatbelts, often get injured by clear air turbulence.
Flight attendants have been killed by clear air turbulence as they hit the ceiling, then fall back down, breaking their neck. As graphic as that may sound, people seem to forget that you’re doing nearly 600 miles an hour in a metal tube, and the atmosphere itself is not smooth.
From additional reporting on this incident, it’s simply a turbulence incident, with an unusually high number of stupid people on board who were not wearing their seatbelt.
Not a 787 problem, more of a passenger stupidity problem.