That's very interesting. Wonder where they picked that up? The Celts were of course VERY well established all throughout Western and NW Europe and Britain by the time of Jesus. Could have migrated to America from any of those European countries, not just Britain or Wales (as their Chambers of Commerce would love for us to believe.)
In the story of course, Brendan does in the end reach a continent. He travels inland in a lovely verdant land for 40 days, and reaches the bank of a mighty river flowing westward, onward, but there meets a young man who gives him a poor report of things, so he returns to the coast and sails back to Ireland.