This really isn’t true. The multiverse hypothesis actually grows out of string theory, and specifically out of an attempt to explain the relative weakness of gravity as compared to the other fundamental interactions. In this particular theory, the reason gravity is weaker is because some of the effect of the hypothetical gravity force carrying particle; the graviton, bleeds off into another dimension, a “brane”. Each brane would essentially encapsulate another universe.
In multiverse theories, branes can collide, and these collisions could cause “big bangs” like the one that fired up our universe. So really, it would be complimentary to Big Bang cosmology, or if true (a very big IF) it could explain the Big Bang.