That kind of change in one year suggests there’s something going in with the poll, not a major change in Americans’ religious belief.
You are right that the poll is probably off but America is on the same path as Europe in terms of being less religious. Even “believers” many times don’t go to church or participate in other religious activities. As older Americans die off, this percentage will drop, sadly. Society is on a secular path and nothing is changing that trend. I don’t like the trend but its true — when I think back to even 20 or 30 years ago, society was much more religious.
.....And this contradicts the recent sucess of “ The Bible “ miniseries.