Is it the age of the other person that makes it kidnapping? Can the parent of another child give her a ride home from school and stop at a store first?
I don't think the law covers this as kidnapping. Maybe someone else can shed some light.
I'm sure you see the difference here in what these two did and the examples you gave. I'd like to add that, maybe it's not kidnapping under the law, but it should be: he is 18, she is 14, AND they crossed state lines. If I remember right they were found in Indiana. That should change everything, why it doesn't in this case is beyond me.