50 BTC was the first block reward. It's fairly common for miners to use a unique public address for each block they mine.
This is why there's no single "Satoshi address". We can only estimate how much he has based on how many miners we believe were on the network in the early days until Satoshi disappeared, or more likely until GPUs started hitting the scene and he stopped being able to mine anything significant.
So, it's entirely possible that owner of this 50 btc actually has a TON more if they were an early miner.
This is why there's no single "Satoshi address". We can only estimate how much he has based on how many miners we believe were on the network in the early days until Satoshi disappeared, or more likely until GPUs started hitting the scene and he stopped being able to mine anything significant.
So, it's entirely possible that owner of this 50 btc actually has a TON more if they were an early miner.