I can't find the article in question now, but the impression I got from an article in Yahoo news a day or two ago was that the whole thing was a hoax - there was no "dark secret"; it was just a way to publicize the documentary. Wish I had a link for you, but I looked and I can't seem to find it now.
And, as long as we're on the subject - I think the thing with "Signs", which I saw and liked but did not think was great filmmaking by any means, is that it was essentially a 50s B-movie, made in the 21st century. It worked better back then than it does now. I think it has to do with the fact that there was a naivete then that we don't have now. Just my opinion.