To assert that existence came from an absence of all conceived categories of be-ing is metaphorically the same as saying that existence (in general) has always been the case, since absolute non-existence is not an entity, state, object, principle, substance, empty container, etc that can serve as provenance for anything. To say absolute non-existence came before existence is nonsensical, since change/time wasn't applicable (there is not an antecedent condition or thing to change or become something else -- otherwise it would be an instantiation of existence). It wouldn't go poof because absolute non-existence is not an entity, state, object, principle, etc, with causal powers. Do you realize how contradictory it is to refer to "non-existence" existing, apart from surgically trying to illustrate another individual's semantic dissonance in that regard? (Though fine if you're just referring to the word existing, but it won't cause the universe to disappear.) Absolute non-existence (in general, when not referring to a specific item like Zeus not existing) is just intended as a clarification for "nothing". Needed when we (people) engage in the idiocy of treating nothing as an entity, object, state, principle, substance, empty container, etc. Except when -- as aforementioned -- "nothing" is used as a confusing label for an _X_ that actually does exist or is contended to. Which 99.9999% of time is very much what you'll discover that someone is employing "nothing" for after their initially vague offering is finally penetrated. And the everyday, casual usages of "nothing" (like "nothing is in the empty room") obviously don't apply to this topic. They're not references to absolute absence of all conceived categories of be-ing.