It’s true that some people have bigger bones then others. Bigger bones of course weigh more, but the total weight of the bones in your body doesn’t make a huge difference if you have large bones or not. In fact the weigh of your bones does not differ much between people. How big and heavy your bones are mostly depend on your height. The BMI chart uses your body height to determine your BMI, so the outcome is adjusted for your height.
If the BMI chart outcome is overweight or obese, your bones are not the reason. If your BMI result is overweight it means that you have more weight than what’s good for your health. It has nothing to do with the weigh of your bones so it’s not a reasonable excuse for being overweight.