"Do all worlds in a universe have to follow the same rules? Why not jars over there, spheres over there?" he asks, indicating each "there" with a hand pointing at different parts of the sky.

It's not like he's insistent that they're part of the same universe exactly, just confused. Enough people have suggested there is more than one universe, just like there is more than one world. The latter seems obvious, but the former not so much. If there are more worlds than there are stars in the sky, why does there need to be more room for all of them than what's up there? Isn't all that a lot already?