[Gettersaga]

It's how you are saying
"This is quoted from Dazai, isn't it?"
It was quoted from Otogizoushi, in fact.

If you really understood the sentence immediately preceding this one, you shouldn't have too much trouble. Hope you sensed the light humor in it.

I had perfectly understood the meaning of the previous sentence.

The preceding sentence, in summary, says that people think that all ogres （鬼） are creatures of ugly and detestable nature, but at the same time, people use the term 鬼才 to describe the authors of the highest rank.

I had understood it exactly in that way.
I disn't understand how to connect and translate masaka to demoarumai. Dazai, sometimes, uses sentences extraordinarily long. And it is a sentence, well a series of sentences connected each other, really long.
So I started to think to tne most unbelievable ways (and they were all unbelievable, every time I thought how to translate it I complicated more and more all) to read that sentence in the whole context.
Thanks a lot, Nagoyankee.