This study is looking at the appendix, not any brain tissue. Without considering symptoms, it's possible that altered PrP expression and/or folding in the appendix does not cause vCJD or result from exposure to PrP(Sc).

Also, these antibodies are not very selective for a given confirmation. Idk how this made it into the BMJ because standard in the PrP field is a protease resistance assay given the issues with Ab specificity.