Did you ever take the driving test here for your license? Do you think the policeman beside you will give you a passing score the moment your vehicle moved without your seatbelt on? I don't know where these questions are coming from, more so the person asking such question.

Seatbelt is for your safety. Period. Even if you are parking your car, or looking for a slot, it is your responsibility to buckle up. Simple rule of thumb: If the vehicle is moving, you should buckle up. The police officer found you driving and putting yourself at risk of getting hurt, hence the fine. You should be thankful enough to be reminded, than put this nonsense question.