That's not quite correct. The west refers to socialist states run by Marxist-Leninist or similar parties as "communist," because those are the most geopolitically relevant representations of communism historically and presently. "Stalinism" isn't a thing, the ideology is called Marxism-Leninism and Stalin's contributions are minor compared to Marx and Lenin. The reason anarcho-communism isn't mentioned is because it doesn't exist anywhere that would require the news to report on it.
Westerners see rising socialist success stories like China, and the news apparatus does its best to either discredit China or pin all of its successes purely on the marketized sector, rather than the cohesive socialist system that marketizes underdeveloped industry and socially owns the commanding heights of the economy. Their goal isn't to discredit the left by associating them with China, their goal is to dissuade the left from following its example.