Remote Handset pairing to device (again) ?

I just borrowed a NAC-N172xs from my dealer to try in another room, but it has the 'wrong' remote handset.  I found the posts from 2014 which told me then to press  AUX + i + 5 all at once... and it worked OK.

So here's my question... when you send this key combination to the preamp (N172 in this case), what exactly is changing?  Is the preamp changing it's code page setting to align with the remote handset, or is the remote handset changing itself to align with what the pre wants to see ?

For those amongst you who might think "Who gives a xxxx", this is one of those questions that'll keep folks like me awake at night.  If you think that's strange... you're probably right... and I probably spent too many years trying to communicate with computers (or was it communicating with the users that befuddled my brain?)

Roger