Well then doesn't every major metro area in the United States have its own dialect? How is this "emerging"? It's probably been like this for centuries.

What's "emerging" here is that anyone in the media now wants to mention this particular dialect for political reasons. The title of the author is: "Race + Equity Editor". Why divide people over something so subtle? It's not that unusual. There is no such thing as a common American English for this to be distinct from.