premise: Mosquito County (also labeled on maps as Musquito County) is the historic name of one of the early counties that once comprised most of the east part of Florida. Originally Mosquito County covered the entire eastern part of Florida area presently including all of Volusia, Brevard, Indian River, St. Lucie, Martin, Seminole, Osceola, Orange, Lake, Polk and Palm Beach counties.
hypothesis: Mosquito County is not an official name, but a name used to refer to certain parts of Florida.
reason: The statement doesn't say "Mosquito County" is an unofficial name, but infers it. I think it's tough for the system to see these intricacies.