Yes, you are right, it is not a MP3 file.
My main problem wasn't that it doesn't work, but the lack of debugging
options.
It would be nice if rhythmbox could display the tags of webm containers
with opus audio (like id3info), or if it would somehow tell you that
test.mp3 is not a valid mp3 file.
Public bug reported:
Please note, that I'm not 100 % sure if this is a bug in rythmbox, it
could be a bug in id3v2 or in youtube-dl, but I think it's in Rythmbox.
How to reproduce:
Step 1: Run the following commands:
sudo apt install youtube-dl ffmpeg id3v2 -y
youtube-dl --extract-audio --audio-f
