The volatility IMO is due entirely to the hard fork. A big player (likely miner) sold at 450 because they know what is coming.
The most obvious explanation is Mike's ragequit, which got wide exposure in the media (NYT, Motherboard, TechCrunch, Reuters, ...) It was also
commented in Chinese forums. I can't think of any other suiltable explanation for the sudden drop.
After all this time, prof Stolfi hasn't learned TA. Mike's drama made the drop deeper, but it was coming anyway.