This address has currently the most bitcoins of all other addresses. If this is one person then he has $1,8B worth. But what could happen if he sold all of his bitcoins? He surely wouldn't get 1,8B. I believe that from the first 10.000BTC he would sell the marketing would start to fall...
Let's ignore the fact that those are not just some single entity funds as others have pointed out already and focus only on the actual sale.
A dump of all those coins wouldn't be that bad as you assume for the market, the price will indeed crash on that exchange to zero but it won't really affect other exchanges that bad until and if those that would have bought coins at a few $ will start selling there.
Basically, the owner will simply sell a lot of his stash for pennies, pulling too little fiat out of the exchange with that move, and leaving enough to raise back the price. A constant wave of 1000
BTC would be far more disastrous as he would pull far more $ out of buyer's pockets with those waves, dropping the price little by little and leaving fewer funds for a bounce back.
Second thing, Coinbase holds 4 times more bitcoin in their wallets.
But because they are not storing them in one single address, nobody cares about them
There is always a risk to get caught when stealing in general. But considering only 80k from 850k did not move yet... makes you wonder. They stole 6% of total mined BTC at the time
The 80k
BTC wallet if from a different hack, it happened in 2011, here is the
funding tx from 2011.
The 850k is from the 2013 "hack" and those are all over the place.