Here's an odd one?

Do you remember numbers?  Well, some of us can, and some cannot.  Fine.  Do you notice how - a month after you've moved home (and changed 'phone number) - you can't remember the old one?  Good eh? - some sort of auto-delete function going on there.

Well, here's another one for you.  My students - UNFAILINGLY learn their log-in numbers at College (about 7 digits, I think) by the number's position on the keyboard, when they are sat directly in front of it - AND NO OTHER METHOD (they don't actually know the numbers).
If I move the keyboard (to sit next to them and type) they cannot log-in, and they most definately cannot recite their log-in numbers to me.
So, those who have grown-up using numbers on keypads more than anywhere else - predominantly learn a finger-placement, as opposed to (say) remembering first, and the repetition of the action coming later.
Does this mean the memory function is by-passed - or is this a different 'sort' of memory being used?