[GTP]

>but I get the feeling it could've happened with any muscle-memoried password.

I can confirm this. Many years ago I had to type for the first time a password on a classmate's iPhone (smartphones were just beginning to become common). The problem was that I didn't really know that password: what I remembered was a shape I was "drawing" onto the keyboard, which involved the numeric keypad... You see were this is going. That event was the one that led me to finally properly memorize that password.