I checked the discussion on this exercise specifically hoping to see this. Yay.
En tilhører is a listener, the "audience" of a radio show are listeners.
As a verb the base form is å tilhøre (which in certain cases you could split up and use like høre til. An item can belong in the kitchen, den hører til på kjøkkenet)
Is it correct to say: katten hører til jenta. And dies this mean the same as: katten tilhører jenta.
Those are strictly interchangeable, but I prefer to use hører til in connection with a preposition and an object (rather than persons). Katten tilhører jenta. Katten hører til hos naboen. The cat belongs to the girl. The cat belongs to the neighbor.
Tilhøre = belong to (ownership)
Høre til = belong to (membership)
In other words, if I understand correctly, in Norwegian, it's perceived to belong to something means to listen to it, or adhere. Like subordination. Interesting.