So in your "no price manipulation" scenario, who placed the 5,000 BTC market sell order that started the crash, who performed the DDoS attack, and was it purely coincidental that they occurred one right after the other?  And what was the purpose of the DDoS if not to induce panic selling by the person who started the crash?

It seems more likely to me that the two events were organized by some individual or group in order to achieve a common goal, presumably to crash the market in order to sell high and buy low.

However, I am open to alternative explanations.