What does this sentence means with areka/あれか at the start?

Question

When reading, I met with a sentence with areka/あれか at the beginning and it's hard for me to understand. Much thanks if anyone can help me understand it correctly (in case I was wrong ).

あれか。貴様は死人で、いわゆる幽霊とかいう奴か。

Context : MC has been transported to another world and a girl saw him fall down from the sky. Then she brought him back to her house while he's still unconscious. After 1 week, MC woke up and the girl said he had slept for 1 entire week, and started to asking him a lot of questions since this is her 1st time to see a man fall down from the sky.

Girl「貴様、一週間眠りっぱなしだったぞ？壮健なのか？まぁそれだけ騒げれば壮健だろうが」

Girl「いやそんなことより貴様に聞きたいことがある。いったいどうやって天から落ちてきた？いや、そもそもどうやって天に昇った？」

Girl「あれか。貴様は死人で、いわゆる幽霊とかいう奴か。 いや幽霊は触れないと聞くが、貴様はちゃんと触れるな。では違うか」 (my guess but not sure: "Oh I know. You're like a corpse when I found you, so you're like a ghost right ?")

Answer 1

In terms of translation, I think あれか translates to Ah, I see or Aha in most cases.

Explaining how is a bit difficult, but it means of course that and it indicates that the speaker comes to see the connection between the topic under discussion (in this case, the interlocutor) and that (in this case, a ghost).

Thus it says Aha, you are a dead man and a so-called ghost, right?.

Answer 2

This type of あれ (often written as アレ in katakana) has been discussed in the following questions.

• Meaning of 〜あれだ
• Meaning of これってアレ
• Understanding だった的なアレ

So this あれ ("that") vaguely refers to an idea that should be understood without explaining it in detail ("that idea", "that thing you know", "that thingy", "you-know-what"). Here, あれ refers to the generic idea of ghosts, what people usually understand as so-called ghosts. This type of あれ is also written as 例のあれ.

So literally:

あれか。
[Is this] that thing (we know)?
[Could it be] that one?
[So this is...] you know what.