Meh, people often don't really know what to say. And if the other person was heavier than you, maybe your getting into shape made him feel a bit self conscious.

It's good that you are working on yourself, lost weight and are seeing and feeling the difference. The important thing is to keep working on your self esteem, you still carry some hurts from being overweight and bullied so typically you will still be a bit sensitive as that is very normal from working on overcoming bullying and abuse that created low self esteem challenges.