Is your baby okay!!?

So this happen to a me and my co-worker.  I haven't gained too much weight with my pregnancy, I visably look pregnant at 30 weeks I just only have a small belly... I was the same way with my son only gained about 15 pounds doctors weren't concerned then and don't seem to be concerned this time.  But some of the customers that come to my work have asked me if the baby was okay since I'm so small?  I think commenting on my lack of weight gain is just a rude as commenting when a women has gained a lot of weight with their pregnancy!! Are these women who ask me if my babies okay just jealous??? I just don't get why a question like that would be asked!!  My baby is perfect I'm an active healthy human and every bodies pregnancy is totally different and I would think other women, other mothers, would be aware of this.