[1]: https://news.ycombinator.com/item?id=6455391 [2]: https://news.ycombinator.com/item?id=6467393
http://hnrankings.info/6455391/
The discussion you link to shows the usual conspiracy theories, but this seems to me to have all the usual hallmarks of enough people thinking the item is inappropriate and just flagging it.
If you hang around long enough, and pay really close attention, you start to see the dynamics at work. Most people just throw up their hands and shout "Conspiracy! Conspiracy!" and demand answers from TPTB. But frankly, this just looks normal to me.
The other specific aspect of the JustFab stories was that the first one I saw was a complaint submitted as "Ask HN:..." based on what happened to an HN'ers girlfriend. The piece was long enough that it should have been a blog post. In my opinion, it seemed to record a remarkably high number of upvotes rather quickly.
Given the timing and those two other unusual features and the rather mediocre quality of the post, someone may have figured out how to game the HN software's voting ring detection. That would also possibly account for the rapid fall.
I ask myself how many stories about series B funding make the front page of HN? And what are the odds of multiple stories doing so?
To me, the story just didn't seem to have the legs to justify their position. Of course, others who felt similarly may have flagged them, and so the flagging theory for their fall remains a reasonable plausibility.