No presuming necessary. In the article, it describes a test involving smelling t-shirts in boxes.

She was able to detect a person who they thought was a false positive and turned out several months later did have Parkinson's. She detected her husbands before he had signs as well.

They also found the molecule she was smelling which was expressed with sebum. This isn't entirely unfounded as they already knew about dogs smelling cancers and other various diseases.