Well, she doesn't say that the posters are deranged, does she?
The phenomenon of a topic catching on and spawning many threads is what she's on about. Though I don't remember Madeleine McCann having a topic, and many more threads were deleted - barely any remain, because posters would keep posting the batshit from elsewhere on the internet.
That used to happen with H&M threads too (and there's a world of crap out there that's simply not permitted, but posters used to keep dragging it over)
But now they're still standing, because they're commenting on what Harry has put in to the public domain, and, as Justine says 90% is sensible comment (the rest must be the memes thread!)
The Royal Family wasn't set up for this though
It was created in 2011 ahead of the Royal Wedding that year, in response to user demand then