It's fear driven advertising with no meaningful information. They don't mention the cities and I wasn't able to find them. The article is chock full of links other zillow articles, their own products and 3rd party advertisers.
>If you wanted to offer a more convincing doubt about the method, I suggest complaining about their treatment of mix shift.
I'm not trying to convince anyone who will agree on a data-driven premise without actually seeing the data. The article states that a record number of cities have $1m+ starter homes, but there's no easily accessible list of those cities. I couldn't find it, where did you see it? I gave up after clicking about 10 different links and only landing on another vague article or advertiser's product.