DJD
I have seen some cheap "no-name" wheels have air holes in the castings. Wonder if these wheels were corroded and the owner turned them on a lathe to get rid of the corrosion and got into some air pockets.
Also Stockton Wheel in Ca. can repair aluminum wheels that are dented and even have whole sections of the wheel missing. They have a proprietary process where you cannot see where the wheel was damaged even up close. There is no color/grain mismatch in the aluminum. I saw in an old magazine article how they repaired a magnesium wheel that was missing a fist sized piece of metal and you could not see the repair when done.
I had them chrome my old 15x4 & 15x10 Cragars and they came out better than new.
http://www.stocktonwheel.com/widen_straighten2.htm
Dave