Interesting, this usually comes up when a user sees an app listed in data usage with a name like "10xxx" (where xxx is more digits). As SpookDroid mentions, this represents a recently uninstalled app, and is simply showing the data that was used by the app before it was uninstalled. Once the data logging cycle has reset, that should go away. The 5 digit number is the UID of the app (Unique ID).
According to this, the UID range 1000-9999 is reserved for system apps, so what you're seeing could represent some system app that was uninstalled:
https://android.stackexchange.com/q...ves UIDs in range,UID assigned to human users.. This is a bit odd, though, since system apps typically can't be uninstalled (unless the phone is rooted). Do you recall uninstalling any system apps?