They actually released an update at some point that included additional telemetry data recording, just so they can get a better handle on combat logging. It is an illegal offence that can get your account perma-banned at worst, or shadow-banned at best (SOLO play only) (after sufficient warnings are given).
Agreed. It should be.
Incorrect; it's called performing a graceful exit. Meaning when you exit to menu, or desktop via the main menu, the application sends a notification to the ED server of its intent to exit. An ungraceful exit would be when the connection is lost; meaning the server is no longer receiving telemetry from the client. After a time, the server will log this as a timeout; which is an ungraceful exit. Using additional telemetric data, Frontier can see if you were in the middle of combat when you Alt+F4 - additionally, they can use that data to track back and check your history, being able to accurately determine if you are combat logging or not.
It is officially stated, but it wasn't officially stated adequately .. such as an ED FAQ site, or a "Rules of ED" site or something like that. Just because the statement was made on the forums and no where else (to my knowledge), doesn't mean it's not relevant or can be ignored.