@Lexiconical, I'll bite the conspiracy theory angle and add to it.
Maybe the whale is @dan, who's been powering down for a while now. He mentioned recently in the EOS telegram group that he's been talking about Steemit a lot in the past few weeks. Probably giving it as a successful example for what DPoS and Graphene (technologies that will be used in EOS) can do. At the moment, good PR for Steemit (and BitShares) is good PR for EOS.
:-)
If this theory was to be true, then I expect the pump to continue for at least one or two months.
That's an interesting angle I hadn't considered. However, it seems that Dan is a bit down on Steemit lately (since linear rewards) and he seems to be selling Steem lately...