Ric - You are right this isn't an error it is a strike whos center came out and was put back in wrong, this could have been done by a person working at the mint where the strike was made or by somebody who won the strike and reversed the center and turned the strike back in. The only way the strike could be an error is if the mint made another set of dies with the reversed and rotated design, but I don't think the mint would have gone to this trouble or expense.
Walt