How does Garvey put Cole's father in his place?

From the text:

Cole’s father, standing nearby, overheard Cole’s remark.“Son, this isn’t about choosing sides. This is about learning responsibility.”
Before Cole could answer, Garvey said,“Yes, Mr. Matthews, this is about responsibility. By the way, when is your son’s birthday?”
Cole’s father gulped a quick breath, and his face grew flushed.“Uh, well…birthdays have never been a very big thing around our house,” he stammered.“I think it’s the beginning of July sometime.” Quickly he turned and left.