Most of this old wallets can belong to anyone, Satoshi wasn't the only person that contributed to Bitcoin back in 2009-2010, there were lot of solo miners then and some contributors that mine Bitcoin then because even your laptop then can mine then but things have change now because of the difficulties and judging by those wallets, the person only sent Bitcoin from his legacy wallet addresses to a segwit once probably because he change wallet to a modern one.
My questions are the following:
1. People who own hundreds and thousands of Bitcoins, where do they trade? It's risky to deposit such a high amount of coins on platforms like Binance and Coinbase because you aren't guaranteed that they won't block your account, even immediately after you deposit them. So where do they trade?
I'm not sure if you are taking relating to that coin but an exchange doesn't have that right to hold your account for having a large amount, you were verified by the way so they know where to take a lead if something is suspicious but I just think that it's not a good idea to always use centralized exchange for such, it breaks your privacy.
2. How do they convert their Bitcoins into fiat? I know that years ago there were some bank transfer deals on this forum, I remember that Bitmain wanted to sell 10 Bitcoin or something like that here and they probably had a deal with a forum member but today when the price is so high, where do these big holders sell their coins and get fiat in their bank account? On traditional exchanges?
We have decentralized exchange like the hodlhodl that are still in existence today and are working perfectly, you can trade their but I think some people use OTC which is over the counter where you can do bulk of transaction buying and selling without going through the exchanges