Jewish friend marries non-Jewish girl, has a child, and schedules their child’s birthday party for Rosh Hashanah, AITA for being mad?

I understand Judaism may no longer be a priority for this person, but he grew up Jewish, with Jewish family, and in a heavily Jewish area. His Jewish friends and family (which are many) had to choose being going to shul on Rosh Hashanah or being at his kid’s birthday party. I said something strongly implying that it was wrong. Am I the ahole for being disappointed in him?