It wasn't six different tests, it was six tests, most likely keying on the same chemical compound (and most likely not the actual RDX in the explosive).
This could happen from having the detector set too high. I've seen someone at a trade show run a bag of spinach through one of these detectors, and it dutifully screamed "EXPLOSIVE" when it got a hit from the naturally-occuring nitrates in the spinach.
I see what you are saying, but I was referring to the number not the "kind" of test. I apologize for not being more clear. See - If I give myself 6 pregnancy tests, that would be 6 different pregnancy tests (and woe to the company who is wrong 6 times! heh) even if they were all the same 'kind' of test.