Is 夜だから some kind of idiomatic expression?


[![manga](https://i.stack.imgur.com/2Ay54.png)](https://i.stack.imgur.com/2Ay54.png)

In the following dialogue from a manga:

> A: 漫画かよ…！
>
> B: わははどうしたみつや、寝ぼけてた？
>
> A: …別に、なんで泣いてんのって思って
>
> B: うーん、あー、夜だから？
>
> A: 何ソレ

The character wakes up and tells his friend who was crying over reading a
manga "I was wondering why you were crying"

And his answer is "夜だから"because it's night". Is this some kind of slang or
idiomatic expression?




The short answer is no. It has nothing to do with an idiom or culture-specific
phrase.

(Neither of the two guys seems to think that 夜だから is a valid reason in the
first place.)

