Wow. O'Keefe did some serious work that embarassed the Obama administration several times. My guess is one very deliberate key stroke on some bureacrat's computer is the culprit. My guess also it will be near to impossible to find that culprit.
I understand getting off the list is damned near impossible when "accidentally" placed on it. There doesn't seem to be a web form that can be filled out to challenge the listing. In fact, unless one tries to buy a firearm and gets rejected, there's no way to know if one is on the list in the first place.
And it's a felony to try and fail....