Never let a crisis go to waste.
Of course the FBI is going to order stuff they think is useful. And they're going to cover it in the usual law and order gloss. Not that I think stingrays are the best way to spend money, but one does assume that organized crime is also going to look at the chaos triggered by the hurricane in order to do more of whatever it is that they usually do. Therefore the FBI needs to be prepared.
And the will likely use cell phones. Hence the stingrays.
If you look closer, you will undoubtedly find that every Federal agency used Katrina as an excuse to order all sorts of useful toys.