Their "nothing" is just a label. It's not a legitimate absence or non-existence of every type of be-ing that humans have ever discriminated and proposed. For instance, they may select (real or detectable) particles to be their "something" and their supposed "nothing" then referring to a fallow condition of quantum fields. The latter is actually "something" itself in terms of potential effects.
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Frank Wilczek (1980), Stephen Hawking and Leonard Mlodinow (2010, 180) as well as Lawrence Krauss (2012) explicitly claim that this answers the question of why there is something rather than nothing. The basic idea goes back to an issue raised by the symmetry of matter and anti-matter. Given that the symmetry implies equality, matter and anti-matter should have annihiliated each other. Creation should have been aborted. Why is there NOW something (particles) rather than nothing (mere energy in a quantum field)?"
https://plato.stanford.edu/entries/nothingness/#ResConEnt
Legitimate, absolute non-existence would also include the absence of actions (not just "things", substance, an environmental situation or whatever nouveau gibberish addressing concrete affairs). Which is an insane item to have to needlessly highlight, but probably necessary due to our bizarre incapacity at times to grok that "actions" don't float on their own without "something" doing or instantiating them. They're a generalization and occasional "systemic expression of directions/instructions" abstracted from a sequence of different states of _X_ (changes). Subsumed slashed grouped under terms like "running" or "colliding" or "oscillating" so that each individual state does not have to be tediously and impractically referenced.