I would suggest that "very small" is equivalent to "trace amounts"

It appears that the machines don't have an "and" function. Otherwise if it detected above threshold of a common chemical like glycerine, but no trace amounts of other components necessary to make an explosives it wouldn't alarm.

Besides, nitroglycerine is allowed through the checkpoint as medicine.

Something doesn't add up, when it appears that the "wrong" hand lotion is more likely to alarm than GSR from a range session.

Large numbers of false positives are not good for security.

For example, if an ETD alarmed and no explosives are found on the person or in their carry-on, why isn't this person's checked luggage flagged? That would be layered security.