What's your problem? Why is it so difficult for you to understand the difference between gnosticism and agnosticism? You shouldn't even think of it as related to theism or atheism. It's a separate parameter. If you are gnostic about something, then you are convinced that you know the truth. If you are agnostic, you aren't making such a claim.

For example, let's say someone hits your dog with their car, and it causes you to think they did it maliciously. If you are gnostic about it, then you are absolutely convinced they did it to hurt you. If you are agnostic about it, then you admit you don't know what he was thinking, but you are still at least slightly convinced he did it to hurt you. That is completely unrelated from actually being correct.

There is absolutely a difference here. The difference is in the strength of your being convinced. If you are absolutely convinced beyond doubt, then you are gnostic. If you not absolutely convinced, then you're agnostic.

For example, you might be agnostic about the fact that sqrt(2) is irrational, but still believe it. I am gnostic about it, because I know logically that sqrt(2) is not rational.

So, a gnostic person is equally valid a category as an agnostic person. We can apply this to atheists just as easily, because gnosticism is the property of believing in knowledge of the topic, as opposed to accepting lack of knowledge, and there is nothing about atheism that makes it special in terms of whether or not the terms gnostic and agnostic can be applied to it. If there is, by all means show what it is, because you have not yet done so.

Besides, what about the lying internet theists hiding behind faith to shirk any intellectual burden? Compared to the absurd claims they have about the nature of reality, it's a lot more reasonable to say "I do not accept the claim that there is a god, but I am open to the possibility of the existence of one." In fact, it's still more reasonable to say "I know there is no god," because you can logically argue for it much more easily and much more strongly than you can for the opposite.

Last point: I just realised where you are going wrong. You compare gnostic atheists to human dinosaurs. The critical difference in the validity of each is that one of them may turn out to be correct, while the other is trivially disprovable, and also that one of them describes a person who believes they know no god exists, while the other is just a human dinosaur. However, you can still be gnostic or agnostic about being a human dinosaur. You can claim to know that you are a human dinosaur, and if you truly believe it, then you are truly gnostic about it. If you allow for the possibility of being wrong, then you are agnostic. Neither of them makes you a human dinosaur, whereas it's obviously possible to believe in no god and believe that you know there is no god as well.

Need any more examples to prove you wrong?