I think so. They swabbed it with something. It initially went through the machine and then I had to stand around waiting for awhile until they could test it further. There's not any metal on the jacket and the pockets were empty and it was the only item in the bin, so it didn't make sense to us at the time. We assume that the cat urine or multiple washings with vinegar/soap had somehow made it show up as odd. There isn't a stain that is visible to the eye, but I did wash it again when we got home!

Editing: Looks like I was wrong. I just looked at it again. The zip fastener is actually metal, but the rest of the zipper is plastic.