OMG, I just lost it all! No time to recreate.
Basically: it's friendly fire. I think a small number of people who consider themselves liberals/Democrats really do divide the country up into coastal cities versus the entire interior of the country. The original tweet stated that people who live in cities are surrounded by more diversity than people who live in less populated areas. That is undeniably accurate. It then postulated that this means those who live in cities are less likely rather than more likely to be living in a "bubble". That is arguably equally accurate. But instead of picking up there, the linked piece immediately switched back to the claim that it's coastal cities versus the rest of the country.
So, my response to you pointed out all of the spots throughout the center of the country where the entire state was red except for the cities, which were blue. For example: Indianapolis, IN; Omaha and Lincoln, NE; Des Moines, Cedar Rapids, and Iowa City, IA; St Louis, Jefferson City, and Kansas City, MO; Chicago, Rockford, Bloomington, Champaign/Urbana, and Carbondale, IL; etc.
It's not coasts versus interior....it's cities, where there is diversity, versus monoculture.
I also included a link to a relevant Atlantic article: Red State, Blue City: How the Urban-Rural Divide Is Splitting America.
That's as much as I'm going to reproduce, at this point!