Isn't it a myth that having a small baby bump during your pregnancy means your baby will be small?

If one more person says how tiny I am I might go nuts! I’m 21 weeks and I have a bump, it’s just not very big. I was very slender to start with, which I thought would mean I’d show quickly but it’s actually been the opposite. I weighed about 90 lbs before the pregnancy and I’ve gained a little more than 15 pounds since. The doctor says my weight is perfect and the baby is growing just fine. If my stomach is so small, how is the baby “growing”? I can understand why people make comments. If you didn’t know I was expecting, nobody would look at me and think “oh she’s about 5 months prego”. Anyone else have a similar issue? Was your baby born a healthy weight?