I've visted Fez dozens of times and on one visit I stayed for eight weeks learning Arabic.  

There are nowhere near 9000+ lanes and 290km in the medina.  This is an urban myth turned into fact by mindless repetition.  Check out the map at http://www.fez-riads.com/wp-content/uploads/2012/11/Fez-Medina-map-November-2012.jpg