The "ninjamine" along with the allocation and planned uses of the proceeds was described and disclosed in the original bitcointalk thread as well as here: https://steem.io/roadmap/launch-and-sale/

The 'steemit' account has already sold hundreds of thousands of dollars worth of coins, at least, presumably to cover business expenses, most apparently via privately-arranged deals with blocktrades acting as a broker rather than directly on public exchange markets, but likely some of the latter too. There is absolutely nothing wrong with having done so; it is in accordance with the stated plans.