Communists and Anarchists are (were) both leftist because they agree on the problem of the existence class and hierarchy. Anarchists disagree with Communists on the methods of abolishing class and hierarchy. The communists said you must become the state then you can abolish it. The anarchists said that isn't possible because power always corrupts and the ends don't justify the means. History has proven the communists incorrect.
Discussion
I said "(were)" because we're apparently changing the meaning of the word "anarchist" now even though it was first used by the leftist anarchist Proudhon who was born in 1809.