If Satoshi traded his (according to your example) $10 billion worth of bitcoin with Greeks for their property, they would not be any poorer because they'd have all that bitcoin in exchange. They might even be better off since by entering into the transactions they would have increased bitcoin's adoption and hence its value.
Yours is a false argument because your conclusion assumes bitcoin is worthless, which assumption is inconsistent with your premise that bitcoin is circulating with a value of $10,000/BTC.
Bitcoins (or any currency) are not wealth, they are tokens that people can exchange for wealth with other people.
When you are measuring the wealth of one person or company, it is correct to include any currency that they own, because currency is so easily exchanged for other wealth with other people or companies.
But when you are measuring the wealth of a country or of a planet, you cannot include the currency that its inhabitants own, unless they can easily exchange it all with people outside the country or planet.
In that example, before Satoshi spent his stash, the Greeks owned a lot of houses and land, and 9 million bitcoins. After Satoshi's buying spree, they would own a lot fewer houses and land, and 10 million bitcoins. Unless they can use that 1 M bitcoins to buy 10 billion USD worth of stuff from people outside Greece, they will be poorer by 10 billion USD.