I seriously doubt that this is evidence of anything.
First of all, how do you know that this is a single person selling 69k BTC, and not a single person buying 69k BTC - which should have sent the prices skyrocketing instead? How can you tell this difference from the transaction history? - Take a moment to think about it.
The thing is, unless you can link some of the involved addresses to a bitcoin exchange, you can't tell if this is a buy or sell, or something completely different altogether (like someone just consolidating their addresses). The thing to realize is that flows that do affect the market occur at the real-currency side of the economy, not at the BTC side, and could only be traced through data logs of an exchange. - Consider this: if a speculator purchases all their bitcoins at an exchange and sells them all later, without ever withdrawing them, then even a huge sale would not appear in the blockchain - at all.
From the publicly available data, there's one thing we can tell for sure: nobody attempted to sell 69k BTC at an exchange in one go. Even at Mt. Gox, the market is simply not deep enough to allow that to happen. Such a sell order would wipe out outstanding buy orders, causing the price to drop over 50% instantly. That's just not what happened. The drop from $266 to $125 took six hours, during which only some 55k BTC were traded at Mt. Gox in total - and this figure already includes all the sell orders from the panicking public.
