They met in June as reported in many news sites including this one.
For the head of state of one of the most powerful countries on earth to meet a 23 year old developer is unusual. Why would Putin, a master of state power meet, and by doing so endorse, the leader of a community that is antithetical to state power?
There is a conspiracy theory that they cooked up a plan to control Ethereum. That would so obviously fail that it implies that Putin and Buterin are stupid (which is clearly not the case).
Putin clearly wants to disrupt American power any way he can. Disrupting the US$ as a reserve currency is part of this. He knows that the Russian Ruble is not a contender. So why not promote an alternative, however far fetched?
Decentralization will disrupt the power of the corporate giants of the Centralized Internet era, most of whom are American and none of whom are Russian. So why not promote a leading platform for Decentralization?
Russia has a lot of people with crypto expertise who will benefit as this grows.
Of course it helps that that the idea of ETH ("Gas") as a commodity like oil is intuitively easy for the Russian leader to understand.