13000 BTC means nothing in the crypto market or even in the BTC market alone.
These kind of news whenever the market bleeds means nothing, they just try to find that " why the market is bearish ", they simply forget the fact that this is how market works, waves of ups & downs till eternity, old news, nothing new about this.
13k BTC actually means a shit ton of Bitcoins to sell and affects the markets very easily. But combine these 13k BTC sale with the current global situation (health, economy etc) and you'll get a very negative combo BTC has to fight.
And it's obvious people are looking for the reason of market selloffs. You have to be up to date with the news if you don't want to lose money as a speculator or investor.