Who discovered America can only be answered in the plural. It is HIGHLY probable that in the millennia before Columbus, there were many accidental and then purposeful discoverers. Every single one of them is MEANINGLESS to the m modern world. Until Columbus established a continuing relationship between Spain/Europe and America, the fact that Brendan the Voyager ‘discovered’ some place to the west around the 6th century is just as meaningful as this story of the Romans.
Now if they were to use the word ‘encounter’ I would be less vexed! A coincidental and ephemeral visit with no lasting effect!
The story goes that somewhere along the line someone decided to bury immense fortunes on the island. To mark this secret spot they supposedly planted the island full of oaks which identifies it as the secret island so only they know which is the right one because oaks are said to not be common and none of the other islands are full of oaks.
The issue with that is that doing so would be a giant sign saying "Land here!"
Ancient ships often became damaged on long trips. Oak would have been one of the woods most needed to do repairs. Why plant an island full of the tree most valuable to ancient travelers?
Every captain with a successful record of exploration would have a profile in mind of islands they needed to put in on. Besides materials for repair and fresh water a captain would be looking for food for resupply. Oak forests and the surrounding environs not only tend to have a lot of wild food available they also tend to have one of the more valuable things they would be eternally short on, meat. Everything from various fowl and squirrels all the way up through deer, bear, and wild boar (you and I know that there are no boar there but adventurers to a new continent would not know and if there were any they would be hanging out where the acorns are). Nearly every ancient captain would stop here knowing that the islands covered in white birch, tag alder bogs, whatever else there is over there, are not going to be as productive.
Its not just the captain who would have known this via some secret captain training. Not very long ago most of the population were farmers. Everyone close to the land knows that oaks equals meat and not just in the form of wild game they would have collected near their farms. Ancient farmers all the way through modern homesteaders give the animals access to this type of forest if available. One would not want to put anything secret on an island where any advanced culture had access or might settle and nearly every member of every crew passing by would have known the value of that land and why they should land there.
Youre not just concerned with your rival culture taking the island, what about the indigenous peoples? Would it seem wise to you to plant what would be to indigenous peoples the equivalent of a combined hardware and grocery store with free high quality fuel and then run away and expect it not to be inhabited when you return? How are you sure the locals are going to be cooperative when you return? Are you sure youre going to have enough men to take back the island and get your treasure? Even if the locals didn't make any camps on the island, even if the locals didn't think your treasures valuable, would it be wise to draw as many intelligent eyes as possible to your secret? Might they not make an arrangement with one of your cultural competitors?
IF there were any Vikings, romans, irish monks, pirates, basque fisherman, or anyone else travelling through this area they would make a point of stopping here. Planting the island full of oaks to mark your secret would have been possibly the most singularly ignorant thing a person could do to give your secret away.