You can tell a lot about how a stud breaks in regards to the formation it leaves at the end of the shank on your hub. In your case, with the exception of the one stud center w/ the caliper, it looks like the other 4 were far too tight. Whenever a overtighten lug nut snaps, it will leave a smooth little "hill" on the end of the snap. Weakened studs have a much more of a "jagged mountain" that sticks out, like your stud centered with the caliper. When leaving lugs loose, you will get a vibration, with that vibration, you will beat the stud holes into oblonged shapes on your wheel before they will let loose. (notice it a bit on the pic w/ the steel wheel. Stud hole above the one w/ a lug still on it. notice the shiny edge to the left of the hole). Additionally, the studs will look bent at the tips from undertorquing, as if someone "smeared" the tip across.
This has been my experience and lessons in life. Of course, all this from peepin' at a picture isn't the most accurate, but may help you figure out what really happened. As always, I'm glad as everyone else is that no one was hurt. Looks like that SHO definitely absorbed a high speed wreck rather well, considering it lost a wheel!
