what is the function of NSObject in StoryBoard / Interface Builder?

I am currently following a video tutorial course about test driven development of iOS in Swift, but when testing Table View in View Controller, I get stuck, since I don't understand why we need NSObject in Interface builder like the picture below:

Movie Library Data Service is inheritted NSObject class:

the class of MovieLibraryDataService is like this:

import UIKit

class MovieLibraryDataService: NSObject, UITableViewDataSource, UITableViewDelegate {

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return 0
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        return UITableViewCell()
    }


}

and the MovieLibraryDataService class will be used in XCTestCase is like this :

@testable import FilmFest
class LibraryViewControllerTests: XCTestCase {

    var sut: LibraryViewController!

    override func setUp() {
        super.setUp()
        // Put setup code here. This method is called before the invocation of each test method in the class.
        sut = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "LibraryViewControllerID") as! LibraryViewController
        _ = sut.view
    }

    override func tearDown() {
        // Put teardown code here. This method is called after the invocation of each test method in the class.
        super.tearDown()
    }

    // MARK: Nil Checks
    func testLibraryVC_TableViewShouldNotBeNil() {
        XCTAssertNotNil(sut.libraryTableView)
    }

    // MARK: Data Source
    func testDataSource_ViewDidLoad_SetsTableViewDataSource() {
        XCTAssertNotNil(sut.libraryTableView.dataSource)
        XCTAssertTrue(sut.libraryTableView.dataSource is MovieLibraryDataService)
    }

    // MARK: Delegate
    func testDelegate_ViewDidLoad_SetsTableViewDelegate() {
        XCTAssertNotNil(sut.libraryTableView.delegate)
        XCTAssertTrue(sut.libraryTableView.delegate is MovieLibraryDataService)
    }

    // MARK: Data Service Assumptions
    func testDataService_ViewDidLoad_SingleDataServiceObject() {
        XCTAssertEqual(sut.libraryTableView.dataSource as! MovieLibraryDataService, sut.libraryTableView.delegate as! MovieLibraryDataService)
    }



}

and the definition of LibraryViewController:

import UIKit

class LibraryViewController: UIViewController {

    @IBOutlet weak var libraryTableView: UITableView!
    @IBOutlet var dataService: MovieLibraryDataService!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        self.libraryTableView.dataSource = dataService
        self.libraryTableView.delegate = dataService
    }


}

I really don't understand why I need to make that MovieLibraryDataService class

I usually use:

self.libraryTableView.dataSource = self
self.libraryTableView.delegate = self

but why do I need to write :

self.libraryTableView.dataSource = dataService
self.libraryTableView.delegate = dataService