That is simply not true. You are partially correct on Marx’s use of the term, but by Marx’s standards, nothing about the USSR could conceivably be considered communism. Marx was starkly against pursuing revolution without first achieving capitalism. He was against Russian revolution because Russia was not a capitalist society.

That said, Marx was also less consistent on the definitions than some suggest.

Regardless, “communism” was the term decided on shortly after the civil war ended. It was confusing and a poor choice but there was certainly no confusion as to how well it correlated with the idea that communism was a final stage. Nobody believed the USSR had reached a final stage of anything.