Maybe, but that's not what atheism means to most atheists.
Atheism is not believing in God(s). This is different from both saying "I don't know", like agnostics do and actively denying the possibility of existence in God.
Most of us, when we say "I don't believe in X" are not saying "I have absolute certainty that X does not exist". We're saying "I've not seen any reason to believe in X, so I don't". I'm not agnostic about the existence of Santa Claus - I don't believe in Santa Claus. But maybe there really is some guy living in some secret compound on the North Pole -- it is however so exceedingly unlikely that I'm not going to go around answering "I don't know" if someone ask.
Most atheists are "soft atheists" who fall in the category above, who if asked will say "God does not exist," but who if pushed will concede that just like I can't know for absolute certain that Russell's infamous teapot or Santa Claus doesn't exist, I can't absolutely rule out the existence of every conceivable definition of a God.
And this is not an ideology any more than the non-existence of Santa Claus is.
There are also "hard" atheists that insists that God 100% certainly does not, or can not, exist, and in those instances you might be right to call it an ideology. But they're a fringe - personally despite growing up among atheists I've never met one in person.
No the point GP is making is that atheism is a religion (it's not), which is in itself wordplay.
To try to stay on the subject of the article, I find it interesting that it's Protestants who are abandoning their faith which is most of the downward trend in the graphs presented. I find that makes sense as Protestants are generally less dogmatic and more questioning (at least historically they were from my understanding) than their Catholic brethren.
Another way to put it, I feel there are some structural differences between Protestants and Catholics which help to explain the downward trend in one, and less so in the other.
Catholicism is a culturally "thicker" religion, which I suspect is responsible for the trend of lapsed Catholics continuing to describe themselves as Catholic in opinion polls even when effectively Nones. If you operationalized the definition, say by asking "have you been to church in the past week?" you'd probably see more similar trends.
