I think part of the confusion is there are multiple definitions of "atheist". One definition is someone who believes there is no god. That itself is a belief, so in that case your description doesn't match atheist. But another definition of atheist is someone who lacks a belief in god. So then your description would match atheist.
Also there are multiple definition of "agnostic" making the situation even more confusing.
Absolute certainty of any spiritual truth is gnosis, but that of the nonexistence God is not one of the Gnostic heresies (which are specific heresies associated with the specific Gnostics, not a anything which happens to fit the definition of gnosiss.)
But you’re missing the larger point he’s making and the point the article is making, many ppl who claim to be atheist do have a belief system, it’s simply ill-defined. Most atheists arguing in this thread will give answers and do think they know the truth (it’s that there is no god and life is a hedonistic pursuit). And those beliefs build on others and are built on by other beliefs/ideas as well.
You’re making the same argument many make when trying to build on wedge issues: take a tiny portion of a group that is in no way representative of the larger group and then make generalizations to prove your point.
Aside from you (I’m taking you at your word), I’ve yet to meet an atheist who really had no beliefs.
Let me give you an analogy. Imagine growing up in a militaristic society, and the expectation is that you join the military and fight in whatever wars your imperialistic country engages in. Now suppose you do not feel like doing that. Then your community starts asking you, "but then, if you don't fight with us, then who will you fight for?". Do you feel in your life that you have to fight for one particular empire?