Meanwhile, I found it hard to believe that the Bitcoin belonged to a single individual and it is possible that the wallet is a cold wallet of an organization or an exchange cause no one will dare save such an amount in an online wallet.
What part of the article said it was an online wallet? I personally doubt it's an exchange wallet, due to the nature of the transactions, but it's very difficult to ascertain.
If a whale isn't careless enough to store their bitcoins in an online wallet, an exchange would probably know that as well, especially for cold storage.
Aren't these people concerned about address reuse?
Not everyone is very private conscious, considering that the change address is always the same as the sending address in majority of the transactions (the ones I checked out). Probably, they are satisfied with being pseudo anonymous.