Dalton Rector, who was a member of the Northern Virginia Relic Hunters Association and was involved in the excavation of those graves, did five years of research subsequently and probably figured out who those six guys actually were. They were probably Union soldiers from Massachusetts who died during a skirmish on July 18, 1861, called the Battle of Blackburn's Ford.
The 2002 article about his work is at the Connection Newspapers website at
http://www.connectionnewspapers.com/news/2002/mar/27/unraveling-a-civil-war-mystery/