Tried to post what I wrote on facebook but wouldn’t do so. Will try again by editing this.
I don’t see any problem with this story actually being set in the Mediterranean Sea,=. The term in the Greek and Aramaic translates “over against Galila” (ורדו ואתו לאתרא דגדריא דאיתוהי בעברא לוקבל גלילא .) Luke 8:26 may refer to Gallia (France). The south east part of ancient Gaul was called Gallia Norbonensis so if Gadroyia refers to south eastern Spain then that makes sense.
Luke was firstly written in Hebrew then translated into Aramaic and Greek and it is easy for readers or translators to misunderstand the original account in Hebrew. I have written about this in regards to the lost tribes mentioned by St Peter. https://aronbengilad.blogspot.com/2020/01/the-first-epistle-of-st-peter-and-lost.html