I know for sure that the timing of Damien Walter's piece was definitely not because the Guardian knew the details of the Hugo ballot before 11 April. I know this because, in my capacity as Loncon 3's Director of Promotions, it was I who sent that information to the Guardian on 17 April, six days after Damien Walters' article was published, and two days before the ballot was announced on 19 April. I myself saw the shortlist for the first time only on 14 April, three days after the publication of Damien Walters' article (which I don't think I had read until just now).
It is normal practice in media relations to give trusted and reliable outlets advance information of an upcoming announcement (especially if they ask really nicely), on the understanding that it won't be revealed until the agreed time ("under embargo" in the jargon). In this case I admit that it only partially paid off, as fully half of the article discussed the Wheel of Time nomination. I would have preferred the other finalists, including Correia, to get more equal coverage in the piece, and also to have had some mention of the other categories apart from Best Novel, but of course I had no control over what the Guardian wrote, and I was really just glad to get a generally positive story about Loncon 3. In fairness to the journalist, she was probably right to link her story about the (comparatively less well-known) Hugos to the Jordan/Sanderson epic, which many more readers will have heard of.
I don't know why Damien Walter's article (which incidentally mentions Correia in only one of its seven paragraphs, rather lame for a "hit piece") was published on 11 April, fully two months after the debate about Alex Dally McFarlane's Tor.com article about gender in sf; but I'm not particularly interested in that question. I do know that Damien Walter had no information about what was on the Hugo ballot before that was made public on 19 April; he wasn't even on our media release distribution list, then or at any stage of proceedings.
My saying this won't satisfy the conspiracy theorists, but I hope it will reassure the uncertain.