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Yes, it can be called any of these three things; and it is called different things by different people, for the reasons you described.
Three further comments:
Buddhism as I understand it doesn't deny there are Gods (it doesn't say "there are no Gods") so it isn't atheist. But it also doesn't say "God can save you" in the way that Christianity does, or that "The purpose of life is to obey God" etc. The importance of Gods is de-emphasised, people are responsible for their own karma and their own salvation, so it isn't exactly like a Theistic religion either. The story of Siddhartha's going forth and so on is told (at least n the West) as a more-or-less human story.
Bhikkhu Bodhi's book In the Buddha's Words has chapter titles, "The Human Condition", "The Bringer of Light", "Approaching the Dhamma", "The Happiness Visible in This Present Life", which are this-worldly and human rather than other-worldly and Theistic.
Calling Agnosticism "ignorance" is a bit confusing when it's applied to Buddhism. "Agnosticism" means (etymologically) "without gnosis" or without knowledge (of God).
I might describe myself as "agnostic about God" if I have no personal knowledge, no personal experience, of God.
In the West people use "Agnostic" as a middle way between theist and atheist: "theist" means, "I believe in God"; "atheist" means, "I believe there is no God"; and "agnostic", "I neither believe nor disbelieve, I have no personal knowledge of it." (I probably wouldn't say that I'm "agnostic about Antarctica" -- I believe it exists although I haven't experienced it personally).
"Ignorance" is a term which features in Buddhism too: AvidyΔ (Pali: avijjΔ). AvijjΔ too means "without knowledge".
In Buddhism, though, it isn't used to mean "ignorance about whether God exists" (because, IMO, whether God exists isn't the important question). Instead it's used to refer to ignorance of dhamma, ignorance of right view, ignorance about topics like anatta (i.e. whether the self exists), anicca, and dukkha, and so on.
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You may have heard of "sabbe dhamma anatta", the Buddhist teaching that "all phenomena is not-self". A complete discussion on the topic can be found in this answer.
Basically, there is a self, but it is not standalone or independent. Rather, it is changing, arising and ceasing, dependent on other conditions. There is no permanent eternal self.
Buddhism can be considered theist, if you take into account the teachings on the existence of beings called devas and brahmas in the higher realms. Also see this question.
However, Buddhism can be considered atheist, if this refers to the non-existence of a permanent eternal God, because that would imply an unchanging permanent eternal self.
Also, Buddhism can be considered agnostic, if you are looking for an explanation on the origin of the universe and samsara. Was the universe and samsara created by someone or did it appear on its own or was it always there eternally? This is not commented on in Buddhism (see the Acintita Sutta and the Parable of the Poisoned Arrow).