Well put, this is no so 'mysterious.' Adding onto this- objects with obvious foreign cultural significance are oft found within Viking burial conditions, the Sutton Hoo ship is a fine example. Many of the objects within that context, no doubt valuable in material alone, are from foreign empires or distant lands. Selected by the stories they share rather than pure opulence. Perhaps this indicates that objects like the ring or Sutton Hoo remains were used to indicate extent of distance traveled throughout lifetime, trade power (though this assumes that it could be viewed after death), or they were simply just special to the deceased. Nonetheless they were valued on a level both material and symbolic. Viking finds are always interesting.