There are two little dogs on the vacuum pump and two of the same on the power steering pump. These are then connected via a plate with slots shaped like a cross. The dogs on either pump can wear out and break off so I would guess that either the power steering pump failed internally or the connection between the two pumps failed.
I did see three teeth break off of the vacuum pump gear on a '97 once though. I never could find any reason for it. I pulled the gear cover and found only the teeth and no missing bolts, no bound up pumps or anything. The thing made quite a racket when running and was driven from North Dakota to Utah this way. It wasn't the KDP either. Strangest thing!!