Why are some people so rude?

Chontey • Mom to Juellz, Micah, Marvin Jr. & Ta’mar 💗🙏🏽😘
So today I'm walking to get my son off the bus. A lady stops me and says aww your belly is cute I thought you had him already. So then it goes from nice to mean. She then says how many weeks are you? I told her 29 weeks and 5 days. She goes omg your so tiny for 7 months, how much does he weigh. I told her the dr said about 2.9 lbs I have to go for sonogram so they can see his size soon(now mind you on glow it says 2.2 lbs) so she says to me your to tiny, do you even eat, is your baby okay, my baby was 5 lbs at 7 months. So she did hurt my feelings because I'm a normal size for a young woman my size(I'm a small person I can't help that I'm small) I eat constantly and my mid wife said I'm healthy so is he n that he is a great size right now. So I did tell her that n I did give her look n walked away. I shouldn't have let it bother me but idk I just felt a way because everyone that knows me knows I carry small n my friends say that like she carries small but her babies come out good size. 
Like for example my close friend that's like a sister she's bigger than me(like a average size) I'm smaller naturally her baby came out 5lbs or 6 lbs my first 2 boys were 7lbs 10 oz. and I carry full term. Maybe my hormones are all over but I'll just learn to ignore. Has anyone had someone say something rude or say your to big or small if so share. Sorry for the long post, I only feel safe on here venting because you ladies understand me.