It is the only stake that was mined with privileged information about the situation, and the only stake mined by people in a position to guarantee the outcome by, for example, doing restart when things didn't go their way and then lying about it later.

There are some other acounts that were rumored by mined by insiders with some extra knowledge, but there isn't any real proof of it, certainly not enough for witnesses to take action on the basis of mere suspicions. Moreover, unlike Steemit, the owners of those accounts did not literally go out and "sell" their project to the world on the basis of promises about the ninja-mined stake being earmarked to develop the ecosystem and distribute to new users.