complete speculation on my part, but perhaps it was used on the beach for photo shoots (since it was a manufacturer owned car and you noticed sand).
I can certainly understand how you feel and now that everything has been documented I hope you can spend more time enjoying the car!
For what it is worth, I wipe the wheels on my car with a soft terry cloth every few days to keep brake dust to a mininum and when I wash the wheels I use the same soap that I would use on the paint.
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