Maybe some quantum computer hacked his private key but why only go for 200btc when you could go for multiplies higher.
This is my biggest fear and the worst hypothesis for this case. Hackers having technology at their disposal to break the security of blockchain. The consequences of this would be much more impactful and harmful than a single person losing 200
BTC. It could be the end of bitcoin in this case, as no one would be safe anymore. It is said by 2030 quantum computers would be able to break encryption protocols, including of bitcoin.