On the one hand, I kinda get where you're coming from. I've had times where I expressed a desire to gain weight, and the conversation usually meant "You mean lose weight?" "No, I mean gain weight." "You mean lose weight?"...

On the other hand, fat shaming is so common that your friends probably perceived your statements you want to lose "belly fat" as a passive-aggressive way to make them feel bad about their actual fat. Note you can't really target specific fat with exercise. You can only lose fat by losing weight, and it will disappear where it wants and stay where it wants. You can tone your body to support the fat that's there in a way that's visibly pleasing.