I just got off the Dream and was on this sailing. We had a beautiful day at CC followed by our pirate deck party and fireworks. Not sure why it said we turned around.
It looks like it was the middle of the night. Nassau is close enough to CC that they could have turned around, dropped off the passenger(s) in need of medical assistance and still made it back to CC before anyone not awake noticed.
It is rare, but sometimes the ship stays docked in Nassau for the crew to disembark until late night. It's generally when they have done something exceptional. (I'm guessing inspection ratings?) but I know it is very very infrequent. Any even departing at 2 AM, the ship has no problem reaching Castaway.