I only skimmed the article. It is very interesting and I want to go back to it later, but the one obvious explanation (to me) is that Willy was money laundering. It was buying up bitcoins using USD in accounts that didn't seem to exist. I'm assuming that the bitcoins existed and the trades actually happened -- it would be straight forward to tell from the block chain. The simplest explanation is that someone had a lot of USD that they wanted to launder and they were buying up Bitcoin. This money was put in non-public accounts. At some point they wanted to cash in. This caused BTC to crash.

One could speculate that a naive person might offer a BTC money laundering service without understanding basic economics. The bot is buying up BTC, causing the price to skyrocket. The naive operator is thinking, "Awesome, I'll pocket a cut of this!". Then the very nasty people who were offering the USD to launder suddenly said, "OK, please return it all right now". The naive operator is thinking, "No problem, the price is so high" but then crashes the currency. In fact, once could speculate that said operator ended up with a shortfall and had to make a choice between stealing BTC from other accounts or living with 3 less legs than he was born with.

I'm not saying that's necessarily how it happened, but it doesn't seem that implausible to me...