This is actually addressed in the original HN comment the post links to (https://news.ycombinator.com/item?id=19828702):
> EDNS IP subsets can be used to better geolocate responses for services that use DNS-based load balancing. However, 1.1.1.1 is delivered across Cloudflare’s entire network that today spans 180 cities. We publish the geolocation information of the IPs that we query from. That allows any network with less density than we have to properly return DNS-targeted results.