Going by your link, I'll use myself. I Know (not just claim) god/s (deities) do not exist. I made a statement and conclusion based on what I know and percieve as about life on earth. What information I came across, observations, and experiences to the contrary. I don't know about the universe (stars and planets etc) because I can only conclude what I personally know for myself. The earth isn't the center of the universe; so, it doesn't revolve around us.
If deities exist, it is the claim of the theist because he made the statement. I just oppose to it. If someone said that they are adnormal and I believed they were normal, their opinion is the basis of the opposition of my statement. If there were no theists to make claims or state knowledge of the universe, I wouldn't be an athiest. I'd just, um, be a regular everyday person without no reason nor experience that deities would exist. (I don't have six sense)
I use deities because there are so many definitions of gods from metaphor, creator, to earth, and all. Deities in specific to beings. Not a specific deity.
So, to use your wordings, I make claims of the universe but only out of my perspective, observations, and experiences of it.
Objectively and universally, the question is irrelevant to atheists. We can state what we know or believe doesn't exist; but, making absolute claims of that knowledghe outside ourselves? I only know some theist to claim that. I never heard a Pagan claim it. I don't know how Hindu defines deities more than general knowledge they give to outsiders. I'm sure other people outside abrahamics see deities as real. I'm just going off what I know.