Well, that's a good thing for the time being. Was this a fecal test for crypto? If so, a negative lab test isn't gurantee that the animal is negative, just that a positive was not found. Still, this warrants more time and effort into treating the animal.

Keep the animal in quarantine until this is sorted out. Is the vet considering further diagnostics? What are the symptoms other than foul smelling diarrhea?

Ian