It is a freak occurance, I don't know the numbers (I think like 225 different keys) but there are several of your same key out there, as well as with all cars... Or house locks for that matter,
They make so many of them that it is almost impossible for it not to happen
Do me a favor and compare the two keys next to each other, are they pinned the same? (have the same notches and grooves), if so, then it is an extremly rare occurance, and I wouldn't worry to much about it, try with another friend that has a saturn, it shouldn't work...
Sounds like you and that girl are about meant for eachother
(dont know your gender, but still)
Seems rare that you would meet, be friends, have the same make of car, and then suprisingly and the rarest of all these coincidences have the same key for that make...