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


**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 ?")**




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?_.

