Whilst the outbound track for these seals is random in search of food. When the seals feel it is time to return home they choose a perfect straight great circle route home. (A great circle route is the one that modern airliners use as this is the shortest distance between two points on the globe).
This ability to take straight tracks is found in many marine animals such dolphins and whales and I think salmon. Please note that on nearing home these animals will be using different clues – salmon use olfactory clues (they smell the water near their home rivers) to home on their exact destination.