This is, unfortunately, nothing new. In the past I've written to Will's given email address, firstname.lastname@example.org, about errors in his column. Of course, no one ever writes back.
I just don't understand how a supposed esteemed columnist can get away with making such blatant errors. Perhaps this time there is more pressure than usually to get him to correct. You can help by writing to Will at the above address, and/or his editor Fred Hiatt, demanding objective and factual reporting.