RE: Weird marking
Unless one constantly, without fail, shoots tight (contact) groups and "Robin Hoods," the occurrence is commonly referred to as a "fluke" or "accidental." Regardless the occurrence may be a result of superior shooting or accidental, the terms damage and expensive always apply.
Beware of gauging one's shooting form and the tune of the setup on an occasional tight flyer or a "Robin Hood." In most cases for the average shooter, it is a lucky shot and should be considered such and with a grain of salt.