The author of this article plainly hasn't heard of Michael Moorcock, who's been writing about the multiverse since the late 1960s with stories like The Dreaming City, The Eternal Champion, The Black Corridor, Behold The Man, etc.

https://www.michaelmoorcock.net/

Yes if only the author had read the following article that discusses how the concept of multiverse goes back thousands of years in human literature.

https://yalereview.org/article/de-leon-everything-everywhere