I think too many are reading in too much to the flying aspect. In the fire service, different parts of the Country call various apparatuses different names. Typically, in the east and south, a tanker is a truck that supplies engines and ladders. If a firefighter from the east or south were to go out west and mention a tanker, they did think he/she were talking about firefighting aircraft. Out west, they call the water trucks tenders. Actually a well thought out tweet, imo. If he had only said tanker, firefighters in much of the Country would have initially thought truck. Adding ‘flying’ clarified it, at least for fire service personnel.