I wouldn’t say I heap them in together. At times in my life I have rejected a belief in anything ‘higher’, which fits your definition of atheism, although perhaps my mindset was closer to an agnostic atheist stance, which to me is more along the lines of ‘I don’t believe, but I can’t be certain as there’s a limit to my knowledge’, as opposed to being a strong proponent of the belief that there is nothing beyond death.