Negative Indeterminate?

I took a 5-panel drug screen for pre-employment on Monday 5/10 (immediately after the interview). I was not certain I was clean, but have abstained for 6 weeks, and previous to that I had smoked a bowl a day of low grade for about three weeks, and casually (once a month, maybe once a week) previous to that. My money situation is such that purchasing quick fix sebay was out of the question as well.

I heard nothing from HR for three days, assumed I had passed, and went in to take a physical ability test to prove that I could lift and handle the weight necessary to perform my job. Well, I got there and was informed by the medical officer that my sample came up "Negative Indeterminate". I thought that perhaps she meant "Negative-Diulte" as I had had a lot of coffee previous to the test, and I asked the her "so does that mean I have to take it again?"

She told me that I did not have to take it again but that there were trace amounts of one or more of the drugs and it needed to be sent to the lab for confirmation. I asked her what drugs precisely, and if it was "one" or "more than one". She told me that she could not answer that without the form, which she didn't have anymore (HR had it). The test itself was done on site immediately after the interview and the 5-panel test was on the cup itself. I was instructed to leave before the results were ready.

I've lurked on these forums for a few years and have never heard or read or something like this. Usually the standard procedure is to send it for further testing when it comes up POSITIVE, right? I was thinking that perhaps the line for THC was very faint, and she sent it to the lab as a precaution, but that is just speculation. Has anyone else run into this, or can shed light on what might be happening here?

It was also really annoying because I had to drive an hour there and back just to find out there was a problem, after three days of no one calling to inform me my physical ability test was canceled.