I can't remember my god-damned four-digit ATM PIN unless I'm standing right in front of the fucking ATM. Nor can I remember my god-damned four-digit alarm code unless I'm standing in front of the fucking alarm panel. Human memory is shit, and it is entirely plausible that this person forgot their password(s).
And, I would venture to guess, highly dependent on the individual. I can still recall my high school locker combination from 35 years ago, the Michigan Driver's license number I gave up when I moved to Texas 30 years ago, and the phone numbers of my childhood friends. I never understood the "counting sheep" approach to insomnia; if I'm having trouble getting to sleep, I go through my teachers (in order) in my head. I typically nod off somewhere in the college years.
I also have a history of dementia on my mother's side of the family. I'm hoping that regularly reviewing memories is some form of "exercise."