Atheism is the product of finding fault with the underlying foundation of a belief of theory.
Theism is the creation of an arrangement of ideas / concepts.
As concepts are multiple ideas taken together (from the Latin com - "together" + capio "to grasp"); thus also, a Theory is a group of concepts which create a position or arrangement.
Theo is the Greek root meaning: I place, position, arrange. Theos (θεός) means: that which arranges or "who arranges" i.e., the suffix ὅς (hos) means who, which, that.
An arrangement which is made of many concepts is partial to being nullified if one of those concepts turns out to be false or non-applicable in a particular circumstance.
In general, mistakes in logic occur when people logically induce for a specific circumstance and then mis-generalise that inductive reasoning to a more general circumstance. A silly example is: my dog has 4 legs, my cat has 4 legs, thus: my dog is a cat.
The other major logical error is to misapply a general deduction to a specific circumstance which isn't actually in the 'set' of circumstances that follow a general pattern. For instance: Christians are non-violent; Donald Trump says he is Christian; therefore, Donald Trump is non-violent.
Religious concepts make up religious theory. When key concepts of a theory are undermined by facts, a person will in general come to the conclusion that the theory is wrong. This induces atheism---the denial of a theory based upon the destruction of the validity of some of it's key component concepts.
Atheism is valid when it can be clearly demonstrated that a theory (in question) has basic falsehoods as a core aspect of the theory.
Atheism is a general word which you can apply to any theories including religious or philosophical ones. An atheist is generally assumed to be a non-believer in the God concept; however, that is a specific case only, not the general meaning of the word.
The Dunning Kruger effect essentially the interpretation of limited amounts of data to create concepts and theories which in the light of greater amounts of data can be seen to be unwise. Generally speaking, the effect results from the incorrect belief that certain things are true or that certain truths are the only truths that are pertinent i.e., when in fact, those truths are either: a) minor truths or b) only a fraction of the total truths.
The effect is only apparent to one suffering from it after the new information has been revealed i.e., you only know you're suffering from with the benefit of hindsight.
I don't know many people who haven't come to the wrong conclusion based upon limited facts at some point in their life.
Factually, the Dunning Kruger effect can only be diagnosed when the subject of study has defined answers. Therefore, it's impossible to say that anti-theists are wrong, as it is impossible to say something is true that lacks evidence.
Any theory that isn't resting on evidence but instead only on faith: such a theory isn't valid by default--belief in it is not the dunning kruger effect because there are no limited facts for which you can misinterpret. Fantasy is without any factual basis, so it is not possible to draw the wrong conclusions out of limited fact when there are no facts.
Instead, an idea resting on disfactual concepts is a philosophy. For instance: something exists; therefore, G*d must exist because something can't come from nothing. This is disfactual because there is no defined G*d, just an empty noun.
On the other hand, if you say: Dean must have murdered Harry because Dean & Harry were the only two individuals in the building that day, and only Dean came out alive...Those are facts that can be verified; however, it maybe that the conclusion reached---Dean is the murderer---is wrong. Later it came to light that someone got in through the sewer system and found Harry alone whilst Dean was in another part of the building. The authorities who assume Dean did it are the sufferers of the Dunning Kruger effect.