It says nothing of the sort. Its the answer to a single question, so, jokes aside, a god of Atheism is like a god of not collecting stamps. There isnt anything there to form a portfolio. More likely, it would be part of a wider one. Skepticism perhaps?
In Planescape, specifically in Sigil, there is a temple devoted to dead gods, with members actually taking people to the place where the bodies of dead gods lie until they either revive or fade away. Many have speculated that this temple is unknowingly fulfilling the role of priesthood for the god of Atheism, which feeds on disrupting people's beliefs in anything else.
Bringing this back on topic, the reason why I said that skepticism would most likely be the portfolio that Atheism falls under is because most atheists would fall under that umbrella. Despite what religious apologists think, the vast majority of Atheists are not angry, unreasonable people who refuse to believe based on emotion, but rather people who look at silly claims, come to the conclusion that they are silly and demand better evidence. Much the same as most scientifically minded people. Present good, convincing evidence and they will change their beliefs. I certainly would.
My thesis in philosophy was on the inherent flaws in proving the existence or non-existence of sentient beings who don't cooperate with your experiments. Whether or not something is there can't be proven unless something that IS there decides it wants to reveal itself. Science's focus on experiments that can be repeated by other scientists means it would take a very patient set of higher beings to prove their existence, so we can't have positive proof, and it is equally impossible to prove a negative.
People thus tend to believe based on their personal experience, either for or against. I haven't had a deity speak to me in person, but am not offended by the idea there might be one out there. I havee, however, seen enough things that should have been impossible by current paradigms to be more open to what others claim to have experienced on their own.
All of that said, though, part of the issue is that "atheism" covers a lot of belief structures. For most, they just don't see a reason to believe. For some, though, the very idea of people believing in a god, any god, offends them on a deep level and drives them to attempt to tear down any theistic beliefs. For those people, Atheism really is their religion.
I can now see Xx_VoidCowboy_xX as the new God of Skeptics, Agnostics and Atheists...
"Sweet gig, you know. Unlike the other gods, I gain more power when I'm not believed in."
"PHO alone increases my powers to mid level deity."
The god of not being able to keep his mouth shut to save his own life, insulting people, and being so much of a creep he gets banned from setting foot in any nation on the planet....
I've got a jar of di~rt!
Yeah, some of the really old nature deities are like that. But most of them are the gentle loving sort. Especially in their more modern versions.
The change is simple, and inherent in the term 'civilization', which literally means "city life". Putting nature at a remove makes it easier to see the positive and not notice the negative. It doesn't help that the people who were telling the tales and writing the histories laregly studied in the major cities.
There is a reason "Mother Nature is a bitch" is still a common phrase but is still looked upon nicely.
I like the slogan a while back urging you to remember that Nature is a Mother.