do I know you?

strange conversation yesterday at drinking fountain at child's preschool:

woman who works in church office where preschool is housed comes to fill up cup at drinking fountain while child is dribbling water all over his shirt getting a drink. I have seen this woman, but haven't really ever talked with her. And I don't know her name.

(Without preamble, in very disinterested voice):
"When are you due?"
"End of November."
"Do you know what you're having?"
"A boy."

With full cup of water, woman walks away.

Um, hi?

Is it obligatory to ask pregnant women all their stats if (1) you don't know them and (2) you really don't care?