What is the point of requiring the backup password on startup if it can be reset by fingerprint?

[AC Question]

I have a galaxy s5 with the fingerprint lock screen, which requires a backup password (which i thought was used to decrypt the fingerprints) when started up first time. Recently I have added my friends fingerprint to it so he could do some stuff, but one day he got into my phone after I rebooted it earlier. It turns out there is another option that he used to reset the backup password (figured this out when I restarted the phone after and my password didn't work), but it somehow uses fingerprints. What is the point of requiring the backup password on startup if you can reset the backup password with the fingerprint, then get in?

 

[Tim1954]

Well, you gave him user privilege. He's a much an administrator as you are and could conceivably lock you out of your own phone. Nobody touches my phone. Read these forums from ppl who got locked out of their phones....