I'm one of the older people in my PhD program and I think I was one of the first pregnant people many of the other students had really known.  Because we all knew each other I think their inhibitions about asking questions were also clearly down.  And I got some hilarious ones.  People didn't know about maternity clothes, one person would say I was huge and another that I was really small within minutes of each other, one or two people didn't realize that you could feel the baby move.  And the postpartum belly was a shock to almost everyone...  I only wish all the weight left when the baby left...  So while I vote for this guy potentially being crass, I generally found a curiosity about pregnancy mixed with poor understanding of biology (what are people learning in school!?!) led to some really strange conversations.