Through not choosing, agnostics are atheists. Agnosticism is just a subcategory of atheism, and since it derives from the binary of knowing or not knowing, the only other alternative is gnostic atheism.

Which itself is pretty irrelevant since it implies knowledge of the nonexistence of divinity, which implies it’s possible to empirically disprove divinity, and since it’s not possible to actually prove a negative, gnostic atheism is impossible. Therefore all atheists are agnostic (and all agnostics are atheists).

Whether you identify as atheist or agnostic is irrelevant then, since both are shorthands for “agnostic atheist”