PegLeg,
Everything you found makes perfect sense for a ferrocement boat. This is all accurate data. Here's what I can tell about the history of the boat from your post:
1) It's ferrocement. This means (typically) that is was finished by an amateur in his back yard. This is why the yard name is the same as the owner's name. Also, typos are rampant in the USCG database. My info in there is also loaded with typos. Making a vessel yourself and documenting it with your name as the manufacturer is absolutely legal.
2) Where did you find out where the craft was "said to be docked?" This information is not available through the USCG database. It's hailing port, St Petersberg, can be set to any town in the USA, regardless of where the boat actually is from. This is no restriction as to where you can choose your hailing port to be, including places like Denver, CO.
3) The vessel most definitely did not get into the 2ft of water by itself. Remember all the hurricanes? Remember the storm surge? When a hurricane creates storm surge, the water levels can be 10 feet or more higher than they are right now. It would have had no problem making it into the marsh in 12ft of storm induced surge, especially if it broke loose and was blown in there by the storm.
What you have found is one of the hundres of vessels that broke free of its mooring (dockage) during one of the many hurricanes that plagued the Gulf shores. After breaking free, it drifted around at the mercy of the storm, and the owner had no idea where it went. It was never found because people didn't look up into that particular marsh where you can only go via your air boat (Cool toy!!).
It's not nearly as mysterious as you are thinking. Just a simple case of a boat breaking loose and drifting inland via the storm surge. It's definitely a home-built ferrocement sailboat that was thrown around by one of the hurricanes.