The fact that cops would want to be aware of people using the Dark Web doesn't seem particularly surprising or alarming. When you're looking for bad actors you build up a profile based on previous bad actors. I used to work in fraud prevention, and we found, for example, for our particular product if someone opened an account and then changed addresses within two weeks, there was a pretty good chance it was identity fraud.

Of course there's nothing nefarious about opening an account two weeks before you move to a new place, but it would get you looked at because so many people who did were fraudsters.

The goofy thing about this story is the fact that they circulated a leaflet listing something like this as suspicious behavior. They're going to get buried under bogus tips from nosy neighbors as actual terrorists avoid doing this kind of stuff publicly.