There are two main places where Android apps store files: within an application-private slice of the main filesystem, and the shared /sdcard (which, as its name implies, was originally a removable SD card, but nowadays is just another slice of the main filesystem). What the parent is complaining about is the former (and a per-application directory on the later), which is removed whenever the application is uninstalled (or the user tells Android to clear the application state); and unless you have root on the phone (or are looking at the per-application directory below /sdcard), or the application explicitly exports it, it's not even visible to any file explorer.