I suppose the other side of the question is, even if kittens and babies and rocks are, according to definition, "atheists," the question is, so what? What point is one trying to make here?
Fair question. Please read on.
Is it to counter some bad press or misperceptions about atheists?
I don't think so. If anything, presenting non-sentients as atheists may well encourage further disregard and further unfair criticism of atheism. Even all-out insults.
But it is also intellectually honest and may help clarify and correct certain misconceptions.
"Well, I guess kittens and babies like us, so we atheists can't be all bad, can we?" Other than that, I'm not sure I'm understanding the thrust of this particular argument.
I can't speak for others, but in my case I want to point out the nature of atheism as I understand it and, hopefully, also point out that there is an inherent assymetry between it and theism.
Theism, despite some odd cultural and doctrinary expectations with surprisingly good support, can't happen in a vacuum. It can only exist (or at least be claimed) once some form of god-conception arises or is proposed and there are people around with the ability to express belief in the existence of a literal form of that conception, at least to themselves.
Atheism has no such requirements and requires no effort nor justification whatsoever.
That is a fact that many apologists of theism fail to acknowledge somehow.
One of the most frustrating traits of much of the discussion between theists and atheists is that both sides often end up discussing logic and evidences with various degrees of honesty and awareness of facts, but ultimately neither theism nor atheism has much to do with logic nor with evidence.
They are both aesthetical stances, opposed and mutually exclusive but very assymetric in ambition and consequences. Theism is simply inherently more daring, all the more so when it takes the form of proselitist monotheism. To presume to decide what other people should believe in is no minor audacity.
But social reinforcement is a powerful force, and leads many Abrahamists (and to a lesser degree others) to misunderstandings on the nature and consequences of both theism and atheism. And because not all atheists are well informed, many of us end up repeating those mistakes as well.