I tried explaining my problems with tankies without calling them tankies. In fact, I used their own terminology to describe my disagreement with them. It, uh... well it doesn't make a lot of sense.
George Orwell fought in the Spanish civil war on the side of the Marxists. His army was betrayed by the Marxist-Leninists. After that experience, he wrote 1984, in which a totalitarian government uses "newspeak" to suppress dissent by suppressing the very ideas that people are capable of communicating. I don't think it's a coincidence that Marxist-Leninists describe their disagreements in terms that turn criticism of them into gibberish. I think it's exactly what Orwell was writing about based on his experiences.
Communist is a broad word, and i think we have not the same meaning in mind.
To the very core, communism is to think that private property should be abolished. Marx was the most influential thinker of this, and we nowadays call 'communist' all the thinkers and movments that inherit Marx (Lenin, Stalin, Mao, Trotsky, etc.). But anarchists also belong to the very root of communism, they just dont follow Marx (historically, they belonged to the First Internationale and were banned by marxists, with Bakunin as their main figure).
Horizontal system of governance can be communism in its broad sense if there is no private property. This explains some movments like 'libertarian communism', which are closer to anarchism than to marxism. But yes, if we equate communism and marxism, anarchists are no communists.