Maybe the Russian Central Bank is buying up rubles to attempt to stabilize it? They probably wouldn't be exchanging them for BTC, but may be the ones holding the rubles at the end.

Person A offers BTC for sale for Rubles.

Person B offers Rubles in order by buy BTC.

Binance is an exchange which matches these two offers.

In this scenario, Person A is taking the risk of the Ruble devaluing.

Binance likely couldn't even identify all of the parties if they wanted to.

AMM.