At least, this is what an article I saw in CNN claimed. There are so many things wrong with this, I hardly know where to start.
I think that "anger at God" for an atheist is a far different matter than it would be for a believer. My own experience has been that I created and maintained an idea of God in my mind for almost a quarter of a century, developing countless patterns of thought that I grew so used to that they were practically automatic for me. When I finally realized that I no longer could believe in God, those automatic thoughts didn't simply vanish. I felt angry at the ideas in my mind about God, but I never really thought those ideas WERE God. Had I thought a little under the surface, I would have had to admit that I was angry about my former beliefs and how they wasted my life... but I sort of doubt that this "study" had a check box in its surveys for THAT sort of anger. So they just lumped it in as anger at God.
Hardly a thorough look at the subject, IMO.