[karice67]

^
That was a slight mistranslation. There doesn't seem to be an "indecent recording", just a rather 'sensational cut' of the scene. The relevant part of that interview is outlined in purple below:

Originally Posted by karice67

--But even if you put it that way, whilst "Alto-kun who loves the sky" is certainly appropriate up to a point, from around episode 22, it seemed like [his relationships with each] were the focus of his thoughts and actions, right? In episode 22, he even spent the night with Sheryl...when I spoke to the voice actors [for this book], that episode came up. The clamour it caused is quite interesting.
Yoshino: (laughs). Well, that scene certainly developed in a way that made everyone very concerned about what happened next. For my part, I don't want to talk about it, so I'll leave it to [your/everyone's] imagination.
　When we recorded the dialogue, the key animation and storyboarding had already been done (NB: the animation was still incomplete), and a somewhat sensational rough cut had been selected for the recording. And the reactions from the voice actors, and from the staff on this side of the booth, included quite a few "Oooh...!"s.
　But no, I do wonder what actually happened that night (laughs). Only Alto and Sheryl know the truth.

Spoiler for Original Japanese text:

——しかしです、確かにある時期までは「お空の好きなアルト君」でよかったんですけど、22話の辺りから、 どちらとも深みにはまっていく感じじゃないですか。22話でシェリルと一夜を過ごしちゃうし．．．。今回、 声優さんに話を聞いても、あの話でてくるんです。みんな喧々囂々で面白いんですけど。
吉野：（笑）。たしかに、あのあとふたりの間に何があったか、すごく気になる流れですよね。こちらからどうこう と語る気はありませんし、そのあたりは想像にお任せしますが．．．。
　アフレコは、あの話数の頃はもう原撮やコンテ撮（註：映像が完全に仕上がっていない状態）になってて、ちょ っと煽情的なラフが入ってたりしたんで声優の皆さんからも、ブースのこっち側にいるスタッフからも、「お〜 っ」と、溜息が漏れたりしましたが。
いやぁ、本当に何があったんでしょうか（笑）。真実はアルトをシェリルだかが知ってます。