This fragment may be just a paraphrase.  Some have suggested that Heraclitus may have used the noun nomo/s (pasture) instead of the verb given here ne/metai (to be driven to pasture).  If so, then this fragment would be a play on words between no/mos (law) and nomo/s (pasture): either natural law that drives all things (or all things are naturally driven to law), just as animals are driven to a pasture.