Just a guess, the FBI was looking for crowds that gathered at night, during the curfew. Police watching people walking about day or night is not new. Personally, I think the ACLU should find something else to worry about.
My experience, years ago while in the Navy, has convinced me that nothing we say over the phone or on the net is truely private. It may be legally protected, but it is not immune to prying or interception. If you have something to say that you wouldn't want to print out and put on a public bulletin board, then don't send it by email or say it over a non-secure medium like cell phone.
If you are really paranoid, you'd find a way to encrypt your brain waves.