Problems turning off backup encryption

Here’s my situtation:

Neighbor wants me to jailbreak his iphone 6S+ on 9.0.2 so that he can install XBMC. I’m prompted by Pangu to turn off backup encryption, and then prompted for a password. When he enters in what he says he’s 100% sure is his itunes password, it prompts password incorrect. Now I did log out of my itunes account on my PC, and then had him log into his…which worked fine. He says he does not remember creating a different password, or remeber being asked to create one for backup encryption. Now, this is my neighbor, and has been for over 10 years, Just to be sure everything is Kosher, I did go ahead and verify off his account that it is infact his phone, and that the IMEI and such was clean, so we’re all good there. He was able to log into itunes, and turn off "find my iphone" with no problem, so unless it’s some kind of internet connection error or something along those lines, which I doubt, then it’s definitely a different password.

Now I have done some research into it, and so far the best answer I can come up with is to setup the device as a new device in iTunes, and then do a restore; however, I know he’s not going to want to restore and wipe his phone.

So my question is, what working option is available to correct the problem without wiping the phone? I have been jailbreaking, rooting, restoring, etc for about 10 years, so I do fully understand the processes. I do not own an apple product however, so I’m a little bit out of my element in terms of which direction to go here. Thank you for any guidance you can offer. I have searched through several forums, but so far haven’t had any luck finding a solution that didn’t involve restoring the phone.

Oh one more thing…I also remember reading that the backup encryption password isn’t one that can be reset through "forgot my password" means, or through apple. Is this correct?