You are looking way too much in to this. You don't necessarily have to be by a rail yard or industrial area. I only suggested that you would have more if you did. You can get iron fallout from just driving on the highway and rail dust can travel miles so you don't have to be by a rail yard. Also as someone suggested, the cars are usually transported by rail before delivery, so you have that as well. Just bring it to a detailing shop and they will tell you right away that it's rail dust. Don't bother going to Ford and asking them it's a waste of time. I've owned 12 different white cars and every one of them have had it to one degree or another.
IronX and a claybar are so easy to use if you want to DIY. If not, again a detailing shop will spray the car down with this purple mist and you will see it eat away at the little yellow spots. They clean the car after and poof done.