This. Clear Air Turbulence can strike at any time, and you - as in your body - can get seriously damaged even with moderate turbulence. Few people have ever seen severe or extreme turbulence, including the flight crews, but that can happen as well.
When I was 5 or 6 years old I was flying-sitting with my dad, as passengers, though he was an airline pilot, when we hit a pocket of "dead" air. Meals and drinks were just served. For what was at least 3-5 seconds all of the meal trays floated up, hovered and then thankfully relatively gently settled back down. My dad estimated we dropped 200 feet or so.
But by that argument neither is floating around in the ISS - you're still being accelerated by gravity, you're just in the fortunate position that you have enough velocity not to hit the earth.
If the colloquial term "zero gravity" applies to someone in the ISS, then it also applies to someone in a suddenly dropping aircraft.
