On November 6, 2012, Grayson defeated Todd Long 63%-37% to return to Congress after a one-term absence. He described his victory as "the biggest comeback in the history of the U.S. House of Representatives." Although the two districts had different boundaries, Grayson claimed the House historian had told him that the shift from a 56%-38% loss in 2010 to a 63%-37% victory in 2012 was the biggest comeback in congressional history. - wiki
That doesn't explain how he won, unless you are implying that redistricting was the cause.