When he was forced to liquidate bitcoins he might had to sell more bitcoins than he had bought if liquidity was very low. So the extra bitcoins had to be created from thin air which caused a btc fractional reserve. Same logic applies if he wanted to create a downtrend with a fiat fractional reserve as a consequence.
Maybe I am uninformed well or my knowledge about Mt Gox and its story are outdated but my memory tell me that there were a hacking tentative in this company which has stolen thousand of bitcoins.
His Tokyo-based company, MtGox, suddenly stopped all trading in February last year and filed for bankruptcy. Karpeles announced that 650-thousand bitcoins, worth more than eight billion yen at that time, had disappeared.
He claimed the exchange collapsed after hackers stole most of his clients' Bitcoins. But police say most of the bitcoins held by the company were sent to another account.
Police believe Karpeles knows what happened to the virtual money." [emphasis added]
See: http://www3.nhk.or.jp/nhkworld/english/news/20150801_05.html