Well Maytag you asked for it! I'll take a stab here (pun intended..)
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Let's see if we can get some responses. Wish I could separate your pics for annotation would make life easier., But looking at the first pic of the carnage this is what I see.
First your pressure plate did a decent job of containment could have been worse.
Now look at the 10 o'clock position. You can see the friction disk that remained together attempted to extrude between the gap of the pressure plate. This was repeated @ 3:00 and 6:00 but successfully ejected
At the 1:00 position you can see the friction material crushed/depressed as it impacted the pressure plate bolt flange. Also repeated in several areas.
Notice how all but one (at 2:30 still has a small piece attached) of the friction disk to the hub attaching points separated. Now look at the 5:00 position and you will see the only attachment point that still has 2 rivets. Notice the puckering in the center? This is from a tension break, It appears they all broke simultaneously at the same instant.
In summary this appears to be a high speed event to me.