personally, although going to such extremes seems incredibly silly, i think its not in the grand scheme of things.
honestly, if i did not have a clue about caching, i would find it very strange for a couple of people who are probably looking around, making sure that no one is watching, and concealing a medium sized container to be suspicious. bomb wouldnt be the first thing to pop into my head, but i have not been trained to think that.
if something were to happen (God-forbid!) like a bomb going off and it surfaced that someone had noticed such supicious behavior, the public would have flipped.
they are just doing their jobs.