No, but it's a darn fine chance that each person who did escape from their car after it hit the water was wearing their seatbelt. It's a logical fallacy to assume that if x=y then z=/=y.
Those who both wear seatbelts and those who do not wear seatbelts die in accidents such as this. Those who wear seatbelts have a dramatically improved chance to survive accidents such as this.
You could ask my aunt, since she is alive, about it.
Her car flipped upside down into a water-filled ditch, breaking the windows, and instantly filling the car with water.
If she had had to fumble with unfastening the seatbelt, chances are overwhelmingly slender that she would have made it out.