No, I don't think that's what they meant.
The existence and virulence of the worm were known very quickly; within just a few hours of Nimda's release, Atty. Gen. Ashcroft was on television to say that the government knew of no connection with 9/11.
The various antivirus companies and security experts analyzed the workings of Nimda extensively and publicized their findings. Microsoft put out a patch for IIS.
None of these things would have been facts that the government did not learn "until the stricken companies began firing their security executives."
Maybe this is just reporter's nonsense, I don't know. Were any security executives fired as a result of Nimda? If so, why?
I have to admit, I have no idea as to the answers to your questions. I suppose you could go to that online chat the reporter is holding later today (I think I posted it somewhere around response 2 or 3 in this thread), or just drop him an email and ask: gellmanb@washpost.com.