My suspicion in reading the abstract and intro is that this is a translation issue. Inference informed by:

1) All the authors have South Korean institutional affiliations

2) "Detection of human biofluids such as blood, tears, saliva, sweat, and urine is important for clinical analysis of various physiological patterns" (First sentence, seems to be missing a word)

3) "differentiate patients from the normal group with high sensitivity and specificity" (abstract, patients and normal group is an odd way of phrasing this)

That being said...it had never occurred to me that nueral networks might be a useful way of interpreting spectroscopy data, that is a really cool insight