I don't know how that is calculated but it probably just includes the land. I don't know how much of the mangrove on the north shore has been included in the "land area" either.

If you mean the wikipedia page for Freeport itself then I don't know where the little image comes from. As it appears to exclude the main harbour, the airport, Bahamia and other areas that are administered as part of Freeport I wouldn't put too much weight on it. 

The OSM boundaries looked similar to the ones on Wikipedia until I attempted to improve them. The boundaries I did were very rough from local knowledge. The original settlements that pre-date Freeport were excluded from the newly formed Port Area and so were excluded from the "City of Freeport" relation. 

I don't know of an official source for the current boundaries that is suitably licensed for OSM. When I attempted to read the legislation defining the boundaries of the local government districts it appeared that they were assembled from electoral polling divisions and the polling divisions were only available in maps with a copyright notice that appeared to me (as someone without legal training) to go against the OSMF guidance on what is acceptable for use as a source in OSM.

I would like to do a revision at some point to lower the `admin_level` of these to a level close to what you see for local government in e.g. England and make a distinction between the single level and dual level districts and town areas but without a suitable source I'm not sure how much value there is in this.