You have no obligation to discuss your former relationship with him.
You know that, but I felt like it was easy to be guilted into it in those early days.
So I thought I'd say it.
And I agree with the advice about calling 911 if he refuses to hand over your child. You could also set up that expectation with him. Tell him you will wait in the car for DS (if that's possible) or that you will meet him at the door (if you're worried about netting in a public place because it would mean AXH had to drive DS) and that you will not have any discussions with him, and that you will call the police if he doesn't immediately let DS go.
My AXH pulled the same stunt. He said I owed him an explanation. You. Owe. Him. Jack. $hit.