No, since a person holding such a belief must by necessity lack the contrary belief a deity exists.
Correct, an agnostic is someone who believes nothing is known or can be known about the nature or existence of god. Any god concept or claim that is unfalsifiable would necessitate I be agnostic about it, as I would have to be about all unfalsifiable claims, I would also withhold belief from them all, as that is the only rational position.
More peculiar to religions, since we have other words in English that describe the absence of something, asymptomatic, amoral, asexual etc etc…
I would only add as I have many times before, that in the absence of knowledge belief is not objectively justified. We lack belief in every idea or concept we know nothing about, it cannot be otherwise, then when we learn about the concept we are either content that it is sufficiently supported to justify belief or not.
I was born an atheist, and have remained one as no concept of deity presented has been supported by any objective evidence, or rational argument, that would demonstrate a deity exists, or is even possible.