Marxism-Leninism (precisely it, and in the form it ultimately took under the influence of the USSR) clearly possesses a cult – worship, veneration, and certain things that are very much like rituals, almost exactly corresponding to them. And if I see an animal that looks like a duck and quacks like a duck... So it's not surprising that people see this as a religion – because the cult exists. Belief also exists – but not in the supernatural. So, the definition here largely depends on how this question is resolved.
But to extend this to all atheism is definitely meaningless; such inferences do not apply to atheism as a whole.