Heretics teach a false doctrine while pretending to be part of the religion they are attempting to subvert. This is not what communism is.
Communism, remember, has declared itself opposed to all religion. Not just Christianity or Judaism. All religion is regarded (per Marx) as “the opium of the people” to be stopped “cold turkey” and forced into atheism.
A lot of heresies don’t actually pretend to be part of the old religion. Ba’hai don’t consider themselves Muslim, etc.
And communism is not a religion, overtly. But neither (arguably) is Confucianism.
Like most things human taxonomy fails in the swamps of complication and definitional traps.
It did once. However, if it still maintains any hostility whatsoever to islam, pre-literate "indigenous" shamanisms, Black Fundamentalist Protestantism, or Hispanic neo-medieval folk Catholicism, it hides such opposition pretty well.