We don't have a specific explanation about how we all end up in Vallo - best we can come up with is 'waypoints' and 'because Vallo' when quirks inevitably emerge to send our days off-kilter, but as for whether or not we exist within a multiverse, well!
Our own universe is merely one small part of a larger structure which, again in theory, extends beyond the limits of our observations. That entire structure - as in, the unobservable universe - can include other disconnected universes as well. So much to consider! But welcome, it's a pleasure to make your acquaintance Dr. Ziegler.