Atheist is used here as a catch all phrase for the non-religious. That's questionable.

For example it says, "Some people who describe themselves as atheists also say they believe in some kind of higher power or spiritual force."

I suspect it is agnostics and new age types and alike who claim they are not religious but say things like that. Atheism is a clear and strong self-statement, and I don't find that atheists say things like that.

Who is the author really talking about here - atheists, or a grab bag of non religious people who technically still are religious in my view?

Articles like this don't help when they paint in broad brush strokes.