'97 BMW F650 Front Wheel Damage (From what?)

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I'm looking to buy a replacement front wheel for my F650 and found one within my price range, but it has this weird damage.

I was thinking initially that it lost the tire, but the front and rear wheels that he is selling both have this exact same damage.

Do you guys know what this could be from?

After sanding/polishing it smooth, would this be safe to use off-highway?

E: I've added a few more photos.

I have couple. #short Videos on my YouTube bmw wheels leaking all the time ... bmw wheels are made of unicorn farts so sensitive I see this 2-3times a month bmw wheel cracking ..