Wait a minute. Intelligence agencies _are not_ law enforcement. This is a common misconception. Intelligence agencies do not engage in law enforcement, even though in some nation-states police have access to some intelligence agency information.
My bet is they didn't really consider Anonymous a threat, but just experimented to see how much effort it is to clobber them if need should arise at some point in the future.
Here in Germany, police and intelligence agencies are separated more clearly than in most other states[1]. The anglosphere tends to be rather sloppy with these things.
My bet is they didn't really consider Anonymous a threat, but just experimented to see how much effort it is to clobber them if need should arise at some point in the future.