I guess after the test they told her the results (i.e., you're wrong on 1 person because he's in the control group and doesn't have Parkinson's), at which point she insisted that he smelled the same as the others, and then the journalist wrote that up as 'she was adamant he had Parkinson's'. Or she really did fully believe in her sense of smell as an ability to detect Parkinson's without doubt, at which point it as much sense for her to say a person has Parkinson's as you to say the sky is really blue because your eyes tell you and the journalist simply relayed that. There's various readings of the phrase that can make sense.