Not that dangerous.
100' in a puddle-jumper, 6 kts of wind (or so) enough to give a slight chop to show the surface, but not enough to produce swell or turbulence, and some meagre bank angles. OK, amateurs out for some fun, and they didn't push it too far. Even if their donk stopped, they seemed to have enough smash to be within gliding distance of land.
Maritime Patrol crews fly regularly at those heights, with more aggressive manoeuvring, in aircraft with 120' wing spans. However, they have Radar Altimeters with audio and visual warnings, plenty of training, and a devout coward in the non-flying pilot's seat!