It's going to take a whole lot of convincing to persuade me that only 3% are atheists. Frankly the 33% estimate seems a lot closer to truth. I suspect they are counting a lot of nominals are part of some religion. For example my wife was raised Catholic, me Methodist. I doubt either of us has been to either a Catholic or Methodist church for anything but a funeral, wedding or church dinner in at least 25 years and certainly don't fund those institutions. What do we count as?
I suspect that the vast majority of our friends/associates fit roughly into the same situation as us.