That's exactly what I am referring to. You also see them in early betas when Maps is not loading quickly.If you see the map load sometimes, more noticeable if you have a poor signal, the map is made up of tiles that load to make the full map. I presume this is what he is referring to.
You can see some references to tiles in the MapKit developer documentation below
https://developer.apple.com/documentation/mapkit/mktileoverlay