Some lots straddle the boundary line between different flood zones. If the boundary line touches the building (not the property), then that building is in the higher regulated zone.
City staff do not know how your building is rated, or if there are multiple buildings on the lot, each of which may be in different flood zones, so you were included in the notice. If you know your buildings are rated as being entirely within the "Shaded-X" flood zone, then you can disregard that notice.
Example of Flood Boundary Line
In the example pictured, a flood boundary line touches three buildings (with red dots). All three of these buildings are considered within the more expensive "AE-6" flood zone, rather than the less-expensive "Shaded-X" zone.