I disagree with popa on two fronts. First of all, an aufruf is a simcha (and no, Shabbos kallah doesn’t compare), and I think it is proper for someone to attend and participate in his son’s simcha (I hope popa’s son treats his son-in-law as his own child).
Also, I don’t think popa should be telling his son what to do. If he is old enough to choose a husband for his daughter, he is old enough to make his own decision to go to the aufruf.