Personally I'd remove the blossom rather than the fruit as it doesn't have a hope of setting/growing/ripening before winter. I'd hazard a guess that it's something to do with the transplanting, though I don't know what, perhaps a sudden rush of energy as the roots begin to take hold? This happened to us with a Bramley apple in similar circumstances, but there hadn't been any initial fruit-set, just out of season blossom.