Ummmmm..... according to the ending of WW Link and Tetra sailed NORTH of the Great Sea, not south of it. Get your directions straight.
Anyway, to contribute to the issue we all know that Lineback isnt necesarilly the greatest explorer out there so if it is true that the only link between the World of the Ocean King and the Great Sea is the Ghost ship and the Ocean King then i believe its safe to assume that Lineback never really came from Links world. And yes they are diferent worlds because, for one, people who die in links world turn into poes and people in the WotOK turn into spirits that hover over their dead bodies.