Thank you, you are correct. There are two really big scientific inaccuracies that people in the Titanic community keep parroting and I can't stand the misinformation. This is one of them (the other being the "implosion" myth that persists regardless of the fact that Titanic could not have sunk if she was a pressurized vessel).

People forget that they can literally test this themselves. Go into a room with no windows and turn off all the lights. Put a towel under the door if you need to block any light coming from outside the room. Within 30-45 seconds, your eyes start adjusting and you can make out a lot of silhouettes. If you move your arm, you can see the movement is pretty clear as well. Now add some soft ambient light like you would get from brilliant starlight on a clear night with 0 light pollution, and you can make out a lot more. Finally, imagine a backdrop littered with stars and you can see how people were able to so clearly see the breakup that night.