More likely than not the man merely read some pirate themed literature which sparked the spirit of adventure in him. Not having a ship he simply retold a generic pirate tale from a Penny Dreadful he'd read so the US government would be duped into providing him a free ship to sail on. Knowing that there's plenty of lost loot in the Mississippi the man may have figured it's a great place to look, and he's right, but there is no X to mark the spot on that river. No dying pirate recounted his tale. And no "twenty-two tons of silver and gold coin" 🤣
I looked at the pirate location once, a treasure hunter sent me GE maps. He said the one island is off limits to the ordinary person but could get an access pass through his dad. Interesting also, up the river where the old hideout was, some old Spanish carved oaks visible near the water. Someone apparently floated in a backhoe digging up the area. Dirt was dumped in the water out from carved trees forming a small island (wasn't there before). Gangsters later used it for their activities.