I don't know the secret of making miso stock (dashi) but it does involve a fair amount of shaved dried bonito and it seems other dried seafood and seaweed (for a more intense flavour). I guess the soup you had was because there was some fish trimmings available. I typically use sockeye trimming (I buy the whole gutted fish) and make a dashi with it. Haven't got the right flavour (not enough dried bonito?)