Addresses and money like this move all the time, sometimes people are looking around for them and see them. Many times they do not.
The OP seems to be digging into and poking around old addresses for some reason. I think everyone who gets into BTC does that at some point in time.
6 months ago discovered the chapter "lost/damaged wallets/passwords/keys" in the Bitcoin world. Since then looking for stories, wallets, transactions that are connected with such addresses. So found also this address. But so far no clues whether it's a recovered wallet. I must say there are so many fantastic stories (but also lot of fake wallets, damaged keys). I hope that people who lost their keys can be able to get their coins one day.
One of the best stories is a guy who created lots of addresses, printed the screen output for each wallet on paper and stored them. Then transferred over a long period BTC from exchanges to these addresses (The sum is huge). But he thought that a message plus the signature of this message can be used as private key and all his prints on paper show exactly this. The good part of the story is: one day he will be able to calculate the private keys as each print show several windows where also the txt window is visible with parts of the WIF. What I want to say: 'Your Keys, Your Coins' but understand exactly what private keys are, how they work and test it with small amounts (to an address and from that address to a new address) before you do it with large ones.
Maybe this 5000 BTC account was such a case, the owner was able to 'reconstruct' or 'calculate' his private keys.