Are you sure that OSM offer this service? Is it free? I can't find any details of it- it must be an utter bandwidth killer. Do you know where the details of the service are?
Perhaps a commercial OSM partner like MapQuest, MapBox or Cloudmade are providing the tiles?
Looking at that same tile through my proxy (which is backed by the MapQuest map tiles), it is clearly different data.
Here is mapbox, which is also different... http://d.tiles.mapbox.com/v3/examples.map-vyofok3q/15/5242/1...
Though that answer is over a year and a half old.