I can't interpret but from my observation of TSA ETD practices at DFW yesterday I would suspect the validity of these tests. My bag was pulled for extra screening, the culprit was a ziplock with some candy and cheese crackers. The screener took a used ETD swab and sampled the ziplock bag all while wearing gloves that were potentially already contaminated. I observed the exact same process by a different screener checking a ladies toaster snacks except he tested each wrapped package.

I would at a minimum require the screener to test their gloves for contamination before testing a travelers property and I question reusing test swabs at all.

Edit to add: Just a side note, all the concern over a bag of candy while my CPAP didn't get a seconds notice and my Kippy bag never came out of my bag.