Sometimes for carrier convenience (switch crews' actually) a car or a few will get shoved into an industry track for later switching to another shipper. The idea is to take a wad of cars out with you so next time you do less switching in the yard before you go. Sometimes switching in the yard is more of a pain in the ass than switching out on the line. The idea is to not block that customer's ability to unload/load the cars they've ordered. Most customers don't care, but it generally is their track.