shouldn't the power supply for the empeg have protected the empeg?

Not if it was connected by a wire to the PC (USB or Ethernet), and the PC had a power spike problem. At that point you've got a connected loop to ground and the juice is going to try to travel through that wire and through the empeg to reach ground. Or perhaps the spike went the other way around, trying to travel through the empeg to the PC's ground.

We're not saying that your power spike "for sure" caused the disk drive to fail. It could be any number of other problems, including a drive that was simply ready to fail and chose a moment of bad timing to do so.

You mentioned it was an IBM drive. Did it have the standoffs? It could have been something as simple as that.