Certain emails and messages are sent to the Primary Administrator. This is actually whoever "just happens" to be the first assigned administrator. There have been previous complaints that it is difficult and arcane to change this but I think it's worse than that. This is a kind of secret thing that will be unknown to most users. There is no where in the Moodle interface that indicates there is a "primary" administrator. It was (IMO) a lazy decision. If there is going to be a primary administrator, then this must be explicit and there must be something in the UI to set it.