I think what they mean is that the previous Standard map style, which is produced by Mapnik, was rendered in such a way that the rendering process didn't have a

I think what they mean is that the previous Standard map style, which is produced by Mapnik, was rendered in such a way that the rendering process didn't have access to all of the possible OSM tags. But in the future they can use Mapnik to render more tags than they have in the past because Mapnik has improved in some way.