Was "defenestrated" simply a literal translation, or part of a bigger concept or joke?
After listening to the exchange a number of times, it sounds to me as if he is saying

「2[秒]{びょう}[以内]{いない}に[窓]{まど}から[捨]{す}ててるな。」
Ni byō inai ni mado kara suteteru na.

To break it down:

Ni byō: two seconds
mado kara suteteru: throwing out from/through a window

(the rest of the sentence is mostly structure, and immaterial to this answer)
My translation of the line would be something along the lines of:

[My argument] didn't last for two seconds before being thrown out [a window].

In other words, the translation (though the word choice may have been odd) was a literal translation, while also carrying some of the Japanese intent.
Update:
I asked about it on the Japanese SE, and have determined two things:

I misinterpreted the subject of the phrase- rather than his argument being dismissed, he is referring to what he would do &quot;if it was Nygglatho&quot; (namely, throwing her out the window). This applies to Crunchyroll's English translation as well.
The phrase 「窓から投げ捨てる」 (to abandon by throwing [something] out through a window) is a slangy phrase usually used to tell someone what they can do with an inferior product (akin to the English phrase &quot;shove it up your ass.&quot; So, the Japanese phrase is figurative in a different way than the direct English translation.

An updated translation could be

[Nygglatho? I'd] throw her out the window in two seconds.