Big bang is an explosion of space so however the matter is distributed it's one big bang with one emergent 4 space with all the stuff in it.
There may or may not be other 4 spaces or indeed n-spaces emergent from other big bangs - they would be other universes - present in a hypothesised multiverse.
TFA describes multiple regions. That inflation may not be constant across our entire universe does not make these regions seperate universes. They're present within the same 4 space.
I don't think the term multiverse should be used in the context of the scenario described in the article. Find another term.