85% Certain
We have no idea what the son is getting all mad about in this text. He clearly asked his mother what he was born, and she replied that he was a boy. Well, she replied that she was pretty sure he was a boy, which isn’t the most heartwarming thing to come out of a mother’s mouth.
So, yeah, maybe we do sort of understand where this kid’s attitude is coming from. What exactly does pretty sure mean regarding your child’s gender? Does this mean she raised her son as a daughter at one point, just in case she got his gender wrong? We hope that’s the case.