why the "shouldReceiveTouch" returns "NO", the "PanGesture" still works?

Such as title, I have a superView A and a childView B. The A has a panGestureRecognizer. When I swipe the B, it will trigger the panGestureRecognizer of A. So I return No in the shouldReceiveTouch of A, But the panGestureRecognizer still works whick makes me confused.

I used the following and it seems to work as expected:

class ViewController: UIViewController {

    private lazy var topView: UIView = {
        let view = UIView(frame: .init(x: 100.0, y: 200.0, width: 200.0, height: 200.0))
        view.backgroundColor = UIColor.green
        return view
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let bottomView = self.view
        bottomView?.backgroundColor = UIColor.red
        bottomView?.addSubview(topView)
        bottomView?.addGestureRecognizer({
            let panGesture = UIPanGestureRecognizer(target: self, action: #selector(onPan))
            panGesture.delegate = self
            return panGesture
        }())
    }
    
    private var stateString: String = "" {
        didSet {
            if stateString != oldValue {
                print("State changed to \(stateString)")
            }
        }
    }
    
    @objc private func onPan(_ sender: UIGestureRecognizer) {
        switch sender.state {
        case .began: stateString = "begin"
        case .changed: stateString = "changed"
        case .ended: stateString = "ended"
        case .cancelled: stateString = "canceled"
        default: stateString = "some thing else"
        }
    }

}


extension ViewController: UIGestureRecognizerDelegate {
    
    func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldReceive touch: UITouch) -> Bool {
        return topView.bounds.contains(touch.location(in: topView)) == false
    }
    
}

A gesture only works when started out of the green view. Once a gesture has started then events will be triggered normally as they should, that includes within the green view.