Eh, this happened multiple times with both Anthrax and Ricin.
Identifying substances accurately is really advanced-degree chemistry work in a lab - but you have all this equipment issued for field use now used by people that don't REALLY understand its capabilities.
Field anthrax tests test for substances that MIGHT be anthrax or MIGHT be ricin - and we saw false positives time after time, but also local agencies issuing press releases or giving press conferences that were leaving out the "might" and maybe."
Presumably this test simply test for nitrogen compounds, as virtually all explosives contain nitrogen compounds..however the users of the tests or spokesmen literally thought it was a test for "C4."
Exactly. Crank up the sensitivity on the detector, it will tell you that that bag of spinach you just tossed in is really enough explosive to level Miami.