Normaly if someone moved a segnificant amount of btc to an exchamge should not affect in any way the market. However if people saw the transaction or heard rumors about that, could have panicked thinking that someone is preparing to sell 8k btc on a singal market what could crash the price, and because of that those ppl started selling. That panic might have done a lot more damage to the market then the sell of the 8k alone. But tbh I dom't think it was none of the above.