Is it true? There's a possibility that this is false news since many people wanted to down BTC.
It might result in drastic changes since whales have a great factor in the flow of the cryptocurrency market.
Even if you have expertise in cybersecurity, hackers can get what they want especially if it's a group. That's why it's one of the disadvantages once crypto was adapted to be the main currency or use it as a huge business. One of the results also, people will give negative thoughts about crypto regarding this situation.
We will never know,
But the owner provided a link from his tweet to see the transaction and he is willing to give a reward for whoever can help him. This looks legitimate to me.
And yes, it will really have a drastic effect in the market, this is a huge amount of money and that can drop the price anytime soon.