There is a good chance this was a non-issue. The machines are prone to false positives and explosive residue can mean many things. However, the incident points to how piss poor our airport security remains. The government talks a lot, makes it look like they are doing something (a terror alert color scheme based on Skittles and M&M colors) is arrogant, baffoonish, and downright stupid.
What we need are competent, trained, intelligent, and ENGLISH SPEAKING airport security screeners backed up by a military presence, not the illusion that one is there. What we have now are underpaid illiterates and criminals doing the work of what should be an intelligence operation.