There are no eng translations on mango tv youtube but someone hv explained what happened in comments.

It's like a quick recap through main story. The recap is really good, it makes me want to rewatch some scenes in main story.

This extra story also have compilation of their kiss scenes so there's a high rewatch chances for this episode.

Now, the question is why I gave 1 ⭐ for music
During the recap, there is no audio but you can see the Chinese lyrics. I also noticed this problem in main story.