I noticed the same thing - “port city”, indeed. There are some recreational boat docks on Lake Monroe, I guess.
Evansville IN is designated a “Port City”.
Access to shipping lanes carries more weight in that designation than does proximity to the sea.
Sanford was founded originally because it is at the head of navigation for the St. Johns River. Used to be a big deal, not so much nowadays. Don’t know why the author put it in.