One thing is certain, if I had uncovered any major amount of Bitcoin from the early days, I wouldn't share it on the forum, for obvious reasons. This wallet could belong to a holder, a miner, or even some average joe who had bought Bitcoin in 2010-2012 and decided to cashout their coins now, after recovering their long-lost wallet.
Well the owner of this wallet didn't share it anywhere. It is just that it is impossible to not receive attention because everything is public. There are people but also groups that are always looking at transactions that are happening. Also they try to make news out of anything when activity is low like in summer.
There's a large number of dormant wallet addresses, of which unfortunately a large amount of Bitcoins have been lost forever, reducing the number of circulating coins in the market.
You mean fortunately? Because every other holder benefits from this.