Once you have stopped in a parking lot on your own, he doesn't need a reason to approach you. You can certainly argue the seat belt violation in court (if you didn't remove it until after you parked), but that is a minor one with only a small fine ($179) and no license or insurance points. I'm not sure why you're getting wrapped around the axle on that The bigger issue is that you were driving without a license. That's a MISDEMEANOR. You could go to jail (unlikely). I'd recommend you talk to your attorney.
You're wrong about parking lots and private property in this state. The seat belt (and other laws) apply there. The term street/highway in the statute applies to anything that is OPEN TO THE PUBLIC for the purpose of movement of vehicles.
Private roads and parking lots indeed are covered if they are open to the public.
Note that there's nothing you've said here that makes the issuance of the tickets UNLAWFUL. Just because you are innocent doesn't make the issuance unlawful.