Does BMI change with bone structure?

I am wondering if BMI changes with bone structure. Here is why at 5'3 I weighed 150 lbs, and you would assume I would be overweight, but I wore a size 9, and everyone told me I looked terrific. My aunt who is the same height as me, and was 130 pounds at the time, wore the same jeans.

I then lost ten pounds, and in real life people kept commenting on how I looked thin and almost underweight, but online people assumed I must have been overweight(at 140 lbs I wore a size 6). I mean really, is a size 6 overweight?!

I lost my final ten pounds and reached my goal weight (130) and looked very slim, I wore a size 4-5 in pants.

The confusing thing is, everyone tells me I should be about 115-125 pounds for my height...but everyone also assumes I'm 20 pounds lighter than I really am at any given point. I do not do weight lifting so its not muscle.