Exactly this is worry about big transfer of XRP by any owner especially when price is high as it makes coin seem less reliable and shows how few powerful people can mess with its value which highlights big problem with centralized digital coins.
And yes this is completely different from Bitcoin where its creator huge stash has never been touched proving it is truly decentralized with no single person controlling its price. This is why many believe Bitcoin is best choice if you want coin that is truly independent and trustworthy.

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You are also right if Satoshi Bitcoin moved it would cause massive panic in crypto world because it would shatter core idea of Bitcoin being  decentralized belief currently reinforced by his untouched coins. But with this scary thought Bitcoin remains seen as safest way to build wealth today mainly because it has no single owner and have limited supply and history of high returns proving its value.