Later I read on news that this could be a hack because before this person start moving the Bitcoin he did some testnet transaction on BCH, can't get you the accurate info here because I was confuse myself, later in the day some are spreading news that quantum computer is responsible for this, that the wallet was hacked. I refuse to believe though.
Nobody knows for sure the reasons for moving those bitcoins and people can only speculate on this topic. News sites need hype to attract readers, so they create various rumors about hacking this wallet, for example, with a quantum computer. There is no evidence, only speculation. There is already too much noise on this topic. Whereas the reason for moving these bitcoins could be either a sale or a banal transfer to their own wallets.
BTC-community is extremely sensitive to any news, which can affect the stability of the market.
And regarding quantum computers, while there is no proven fact of the possibility of hacking a bitcoin wallet with this, there is no reason to panic.
Quantum computers still look like another horror story for bitcoiners.