T22T: I never claimed it to be a minhag. My parents told us that they didn’t tell anyone an exact date and they didn’t expect us to tell them an exact date. Nor do I expect my children to divulge the due date. We did tell our parents after the first trimester that we were expecting and a general “around chanukah” or “just after pesach” as the due date.
I agree with you that the case you mentioned the parents had a right to be upset.