I think CNN is talking about the area of heavy flooding up to the rooftops, where the rescues are taking place. The mayor is probably talking about any area that is flooded, even though much of the area visible in the afternoon copter shots apppeared to be street flooding of a few feet, many of them looked to be flooded just slightly above the foundation line, but well below the windows.
That makes sense. You'd think there'd be some minor street flooding just from the rain where the pumps aren't working or storm drains are clogged.