How so? They developed a robust system of worker democracy in a proletarian-dominated state, and social ownership was the principal, ie dominant and rising, aspect of the economy. Using their socialist system, they managed to double life expectancy, eradicate illiteracy, house the entire population, end unemployment, and provide free, high quality healthcare and education to the whole of society. Was it perfect? No, it was real, which meant it ran into problems that stem from existing in the real world. That doesn't make it "closer to feudalism economically."
Feudalism is an agrarian mode of production centered on peasants producing agricultural goods and sending tribute to their feudal lord, and trading the rest of their surplus for commodities in towns or making them themselves. This practice was eradicated by the 1930s in the USSR as combine-harvesting and collective farms were created.
I recommend reading Socialism in Power: On the History and Theory of Socialist Governance as well as This Soviet World and Is the Red Flag Flying? Political Economy of the USSR Today. The Soviet Union was the world's first socialist state, with all the good and all the problems that came from that.