So a CJD test is usually staining a biopsy with congo red and observing apple-green birefringence in the image. This generally works to detect amyloid plaques, which is common to all prions. So unless there was a lab mistake, the prion is localized elsewhere from where the biopsies are being done (FFI, for example, localizes to a different part of the brain) or they were using some other procedure, it's seems pretty unlikely this is a prion disease.