iPod Pictures - pulled off and reloaded differect pics from another iPod

My daughter plugged in her iPod today and somehow it downloaded pictures from my other daughter's iPod and the original pictures I'm hoping aren't gone! I haven't done anything like Restore or anything like that. She did not have Photo Stream turned on for iCloud so that is not an option but I don't understand why photos from another iPod would be arbitrarily put on the device . Any advice from anyone would be helpful! thank you