Why does the "this" keyword refer to the subclass too?

In the following scenario, Main.registerEvents(Listener) is part of an event system of a game API. Let's say it should register any method with the @EventHandler annotation.

public abstract class Spell implements Listener {
    protected Spell() {
        Main.getInstance().registerEvents(this);
    }
    @EventHandler
    public void onMove(PlayerMoveEvent event) {

    }
}

public class Fireball extends Spell {
    @EventHandler
    public void onChat(PlayerChatEvent event) {

    }
}

Generally speaking, since this refers to the current instance, how is it possible that Fireball.onChat(PlayerChatEvent) is registered too?