I think it's a fascinating question.
My present guesses are that it was either the work of a
seriously incompetent forger, a DNC saboteur, or is just
a gag that's been floating around and someone stumbled
onto it.
Barnes is a potential source on the "incompetent" theme.
Hillary is a source on the sabotage theme - she knows
exactly what CBS would fall for.
One the gag theme, I suspect that there are fake docs
abroad on the net that say virtually anything about
anyone. Many become urban legends. Did CBS fall for one?
I wouldn't discount the possibility of it being a deranged DUer either. ;)