You didn't say anything about Sally's Silversides. You said don't feed any fish fresh or frozen...
Also I think you're confusing thiaminase with potential contamination.

... I had a snake get a mammalian parasite from a batch of pinkies once that she eventually died from. I realize that that was a fluke, so I don't go around telling new keepers never to feed pinkie mice just because I got a bad batch once.