My Yorkie has had pancreatitis also but it wasn't nearly that bad.
All people food isn't bad. In fact, that is all Ellie gets.
Pupperoni shouldn't have triggered this.
Maybe the cheese did but lots of Yorkies eat bits of cheese.
It doesn't have to be triggered by food at all but if it is, it is usually fatty meat.
The only test that I know of to diagnose pancreatitis is the SNAP or Spec cPL.
What test was it that confirmed the problem? Lipase level? That isn't conclusive. It is very likely pancreatitis though.
If your Yorkie has to be on a prescription food, your healthy dog should not be. The I/D is probably very restricted in fat which wouldn't be good for the other dog. I'm guessing the vet will keep the Yorkie on the I/D for awhile because it seems to work well for this. Then you may be able to go to a lower fat food from the store. Depending on what percentage of fat your vet wants Sachie on, your other dog may be able to eat it too.