Byrd was indeed a southern confederate kkk member.Unlike Trump supporting kkk members like David Duke later in his life Byrd said joining the kkk was the biggest mistake he ever made and fully supported the NAACP civil rights agenda.
You mean Byrd said joining the kkk was the biggest mistake of his life, because it was politically expedient. It is sort of like Bill Clinton claiming he never had sexual relations with Monica.