AngularFire2's Child_added event returns all data again

Question

Is the child_added event in angularfire different in child_added on firebase?

why angularfire returns the whole list, including the value after child_added, while in firebase it returns l

 this.userList = this.room.getAllUser();
    this.userList.snapshotChanges()
      .subscribe(actions => {
         console.log(actions);
        actions.forEach(action => {
          console.log(action.type);
          console.log(action.key);
          console.log(action.payload.val());
        })

Do I need to check the answer again and compare the key, if in an array? before clicking it?