CNC is the IATA code for Coconut Island
CNC is the FAA code for Chariton Muni
There are so many airprts in the USA that there aren't enough IATA 3 letter designators, so the FAA have issued some duplicate codes for smaller US airports where there is little possibility of confusion whith airports outside the USA, ie airports which never or very rarely see international service.
Officially the IATA codes take precedence, but some US based listings will list the FAA airport, for obvious reasons.
I know it doesn't help the reasons why the Austrian A330 was flying such a flight, but it does at least explain the confusion!