Obviously I have no idea why your neighbor did this but one possible reason that comes to mind would be additional points on a points program. Example, If you get the United Chase card you get 25K points but if you also add and AU during the application you get a total of 30K points. Some of the other cards I have apped for give you like 5K points per AU up to three additional. Most of the cards have no required a SS# for the AU but some do ask for it.
