Did they dump some stolen bitcoin ?
Bitcoin price dropping about 15% after this news released

Most likely to be a dump from the stolen coins, I can imagine that they would try to get rid of the coins as soon as possible.
How many Bitcoin exactly did evolution stolen? Some say 400 Bitcoin while coindesk says $12 Million in Bitcoin? What's the truth?
CoinDesk is known for exaggerating. Read around on reddit and determine your mean.