But that doesn't mean that it absolutely was not God's will. He may have been issuing a punishment, or a warning of some sort. The best we can accurately say is, maybe so and maybe no. It's simply more than we can ever know, at least while we still walk the Earth.
It's far too easy to say and think that God wouldn't do that, yet we must be very careful about presuming His will in either a positive or negative direction. We put ourselves at great peril to assume that He would never never do anything destructive if He thought that humanity needed the lesson. The Old Testament is replete with stories of Divine wrath, and even Christ Himself cursed the fig tree which afforded Him no fruit.
It's all too easy to believe that an almighty yet loving God will do good things for us while never calling out nature for His own purposes. To be sure, Christ Himself also pointed out that the people who died when a tower fell on them weren't necessarily greater sinners than anyone who still lived after the incident. So it's all whatever God wills it, and that's that.
We must remember too that nature, like man, is imperfect. If nature were perfect, no storms would form, and we only get exactly what we needed of Her at a given time. So the storm may have been nothing more than a reflection of nature's, well, nature. Part of the point here is to remind Christians that bad things are not automatically or inherently, except indirectly, of course, the Will of God. Yet it also to remind Christians as well as the world at large that we need to pay attention to these seemingly natural events in that they may indeed be meant to tell us something. The bottom line is that it isn't very outlandish to think of Sandy and the harm she caused as a chance at introspection, to consider how fragile our lives are and how they may be changed by the events around us over which we have no control.
Perhaps that is the lesson in a nutshell. As such, it is all the easier to believe that the Hand of God is behind it just the same.