The Vice headline does not accurately reflect the article. The hypothesis is that interaction between parallel worlds could lead to the observed behavior we currently describe using quantum mechanics.
I'm just spitballing here, may be they are not fully parallel. May be it's one aspect of the universe that's parallel to its counterpart of the other universes. Other characteristics of a universe could still interact with each other, thus making their presence felt.
Only if you're into strictly Euclidian geometries. And don't call me Shirley.
They must be logically parallel rather than geometrically parallel.