Certain groups/bubbles look at their friends who, like themselves, tend to be college-educated, relatively well paid, young, childless, etc. and conclude that everyone is (or at least wants to) move into urban cores. In fact, there is a general migration out of areas like the rust belt and many very rural towns to places where there are more jobs. But the migration into urban cores is mostly fairly specific demographic groups into a relatively small number of elite cities. Which is a notable change from the net outflow as recently as 20 years ago. But it's still a relatively modest shift in the scheme of things.