How did this happen???

holy crap.

someone overtorqued the bolts maybe? even if they were, it seems REALLY unlikely that all 20 would fail at the same time.

someone either wanted his wheels, previous owner was bobo the clown, or is the unluckiest rx7 owner on the planet.
 
apparently, he got new wheel nuts or bolts and they weren't the exact same thread pattern so once they where put under stress they just gave up the ghost on him.