If Russia was both buying Gold at a fixed price in Rubles and redeeming Rubles in a fixed amount of Gold then the Ruble would be a fully fungible Gold-backed currency.
(It wouldn't be wise to run such a fully redeemed currency unless the Ruble price of the Gold for redemption was a lot higher - this is because of the long history of Gold price suppression).
Simply buying Gold at a fixed price puts a floor under the Gold price. But you couldn't put your hand on your heart and say the Ruble was gold-backed unless it was redeemable in gold.
That said: the value of a nation's fiat is affected by how much Gold that nation has in its reserves, so in that illusive sense many fiat currencies have some level of gold-backing.
For now the Ruble remains backed by Oil, Nat Gas and military might: similar to the way that the USD is backed.
Why would Russia buy a bunch of gold and then buy more gold for rubles? Why would that make anyone want to hold rubles? Isn't that the purpose of the plan?