Emptiness isn't nothingness. Emptiness presupposes something that is empty of something expected to fill it, the absence of something not the total absence of anything. Absolute nothingness isn't empty because there's nothing that can be empty. Nothingness is not a something, but people here seem to be reifying the notion.
Yes, that's their point. Pure nothingness, the empty set, has the potential to create the set containing the empty set, and then the set containing that, sets containing combinations, etc etc.
In mathematics, at least, this is not true. For example, a set consisting of the empty set is not empty.