Man, it depends on whatsound you wanna get, if you want the pull of to be more subtle, just lift your finger. If you want it to be louder and clearer, then you must do what your friend does. The only problem with doing it is that sometimes you change the pitch of the first note, it may not be too notorious, but it's there. What I do is pull downwards the string at the same time that I lift it, that way you practically "pick" the next note without altering the pitch of the first one.